The Future of Ground-Based Transportation Systems

Posted by on Dec 4, 2011 in Maglev | 75 Comments
The Future of Ground-Based Transportation Systems

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Swift PRT Inc. (“Swift”) proposes a new transportation system designed to replace or radically augment the use of cars in urban and dense suburban areas.  An ideal transportation system is a combination of speed (200+ km/hr), ubiquitous coverage (stations within a 3-5 minute walk max), on-demand departure (minimize waiting for a vehicle or train), near-noiseless operation, safety, privacy, and cost.

One potential fit is a magnetically levitated system, driven by a linear synchronous motor, and comprised of vehicles that carry only two people.  A two-passenger restriction minimizes weight, while fulfilling over 90% of all journey requests – after all, the average car ride in the US is only 1.2 people.  Larger groups can be accommodated by virtually coupling two person vehicles such that the group arrives at the final destination simultaneously.

By radically reducing the weight versus trains (100 tonnes) and light-rail (45 tonnes) by a factor of 100, the resulting elevated track structure becomes flyweight: a nearly invisible 20cm tall single track supported on columns no bigger than telephone poles.  Vehicles hang below the track for aerodynamics, and so that the vehicle banks perfectly going around curves.  Using such a lightweight system, it is possible to achieve rapid acceleration, and top speeds of 216 km/hr (134 mph) with only a 100 kW (134 hp) motor.  Energy efficiency at car speeds (100 km/hr, ~60mph) can be 800+ mpg owing to weight, size and streamlined shape.

A full system-level simulator was created.  This starts with an editor tool built on top of Google Maps to rapidly layout and prototype realistic networks.  Next is the construction of a formal graph, and calculations of the physical limits determined by network geometry, namely centripetal force and track length.  An end-to-end routing system was created which ensures velocity continuity of the vehicle and enforces a minimum 10m spacing between vehicles.  Traffic shaping algorithms were designed to minimize total travel time of all vehicles in the system.  Such algorithms are difficult given that NP-hard nature of the problem which reduces most closely to a multi-commodity flow problem with integer values.  Ultimately the problem can be reduced to a time-slot packing algorithm similar to the bin-packing (or knapsack) problem.

Applying traffic patterns to the simulator allows system-level phenomenon to appear.  In a Stanford University plus Palo Alto downtown test network consisting of 18 stations, 25km of track, a top speed of 216 km/hr, and acceleration rates of 3.0m/s2, capacity peaks at around 2000 vehicles per station per hour.  Trip times are 3-4x equivalent drive-time comparisons between the same points.

Both speed and network capacity were discovered to be ultimately limited by two factors: radius of curves/turns in an urban setting and the “single lane road” problem of any track based system.

Urban and suburban settings are filled with 90-degree right-angle turns.  While vehicles can travel 200+ km/hr, they must slow down to 10-30 km/hr around corners to such that centripetal force (velocity2/radius of the turn) is limited to at most 0.5 gees.  This in turn requires large buffering times (5-10+ sec) to be placed between fast and slow vehicles, such that a fast vehicle does not overrun a slower, turning vehicle.  Such buffer time requirements can reduce theoretical carrying capacity 10x versus the naïve assumption that vehicles can be spaced just a few meters apart.

To avoid this “single-lane-track” problem and decrease vehicle spacing to a few meters requires the use of long acceleration and deceleration on-off ramps.  However, such on-off ramps effectively double network costs in urban environments where station spacing on the order of 1-2km is desired: it takes nearly 600m to accelerate to 200km/hr, and another 600m to decelerate.

Costs were analyzed with the help of experts in structural engineering and magnetics, along with calculations of raw commodity costs, and comparison to ski-lift construction costs, which the elevated guide way most closely resembles.  A cost of $5-7m per kilometer was estimated, before stations and vehicles, and perhaps $8m per kilometer with stations and vehicles.  While this is far better than light rail systems ($30-50m per kilometer), and approaching the cost of interstate highways ($4-8m per lane per mile), it is still far more expensive than non-highway roads.  These can be built for $100-300k per mile on flat terrain (i.e. 50x cheaper), excluding land acquisition, tunnels, and bridges.

Given a cost of $8m per kilometer, stations must serve about 8,000 people each to be economical.  This in turn means stations must be placed at least 2.6km apart even in dense suburban areas (2000 ppl/km2).  At this spacing, average time to walk to a station is around 10 minutes.  At 10 minutes walk to a station, plus 10 minutes walk to a destination, it is faster to drive a car parked right outside your home directly to your destination for any distances under 32km (20 miles) even if the maglev system averages 4x better velocity (as Swift simulations show is possible).  Time to get to a station (walking, or drive plus park) kills the effectiveness of most personal rapid transit and light-rail systems until you have a population density of 5000+ ppl/km2.

While a 3-4x velocity improvement, 800+mpg energy efficiency, and 3-4x reduction in cost over light-rail systems, it’s not enough to displace cars.  The future of transportation is still the concrete and asphalt road, for the simple reason that at $17 per tonne of asphalt versus $900 per tonne of steel or $10,000 per tonne of copper, roads are the only thing cheap enough to be ubiquitous in lower density areas.  Not even the ultra lightweight track of Swift looks cheap enough to displace roads outside of dense urban areas where, because it uses a much smaller rolling stock (number of vehicles) and can have higher throughput, mass transit is likely a better approach.

If roads are the future, then so is the self-driving car, functioning like an on-demand taxi system, connected into a centralized traffic database to avoid congestion and minimize time, and driven by computers in a platoon formation of 5-10 cars to minimize aerodynamic drag by up to 35%.

It is quite possible the same system-level traffic engineering algorithms developed at Swift can be used in such a self-driving system.  That said, Swift PRT as a maglev concept will be abandoned.  No track-based system (not maglev, not light-rail or metro systems) can compete with the cost and ubiquity of roads for population densities below 5000 people / km2.

Table of Contents

Existing Transit Systems:


We live in the age of automobiles.  Cars define our landscape: in urban areas one third of land is used for roads, alleys, driveways, on street parking, and parking structures.  In suburban areas, the average two-car garage represents nearly one quarter of the enclosed “living” space of a typical American home.  Transportation defines how cities are built, and any city whose dominant growth has come since post World War I has been built for the car.  While public transit provided 50% of all urban trips at the end of World War II, it now provides only 2%[1].  Cars dominate.

Yet cars are relatively slow, with highways speeds of 100 km/hr, they define our radius of interaction: where we live versus where we work, the viability of our friendships and romantic relationships, where we shop.

Cars are energy inefficient for two reasons: weight and aerodynamics.  The average trip in the US is 1.2 passengers, and nearly as low in the UK and Europe.  That means moving a 1500kg car to transport 100kg of passengers (15:1 ratio).  Estimates show less than 0.5% of the energy in gasoline is used to move the only thing that really needs to be moved: you.

The other major inefficiency in cars is aerodynamic.  At 100km/hr, half of the cruising energy used is moving air.  Cars average a drag coefficient of 0.3 – 0.4.  A perfect streamlined body can be 0.06 (i.e. 5x better).  Because cars are “flat” on the bottom, they are at best half a streamlined body (0.09).  Along with drag from wheels, mirrors, and the shape determined by putting a motor and crash safety element in the front, cars will not reach half a streamlined body anytime soon.  Further, the larger the car, the larger it’s cross-sectional area.  Drag scales linearly with both drag coefficient and cross sectional area.

Beyond speed and energy issues, traffic fatalities kill 1.2 million people worldwide each year[2], and injure far more.  Beyond loss of human life is loss of time: commute time averages 24.3 minutes each day (over 100 hours annually) in the US[3].  That’s 20 billion hours in just the US, or with an average wage of $25/hour, $500 billion wasted in transit.

Construction costs for new highways run $300k per lane mile for simple rural highways[4] to an average of $8m per lane per mile for a new interstate, excluding the cost of land acquisition, tunnels and bridges[5].  The later is remarkable – it means that 6-lane highway you drive on cost nearly $50m / mile to build.

Trains & Mass Transit:

Advocates of mass transit often claim taking the train /metro / subway is faster than taking a car.  Looking only at average velocity from station to station, they may be correct.  But what never seems to be taken into consideration is total trip time: walking or driving to the station, waiting for the train, transfer to another line, waiting again, walking to my final destination.  It’s the wait times that kill, particularly off peak or weekends.

Real Cost = Fare + Salary (Time to station + Time from station to destination + Transit time + Wait time for train)

Schedules also change based on day of week or time of day.  Understanding this chaos, particularly if you’re a visitor to a city is difficult.  Add a transfer in, and your wait times can double.

Mass transit is also noisy (no one wants rail tracks near their homes), and expensive.  Light rail systems run $30 – 50 million per mile.

What Transportation Needs:

What is needed is a transit system that has the benefits of both car and trains, without the problems.  If we were going to design a system to replace or dramatically augment to 100-year dominance of cars, such a system must be:

  • Fast: Reduce my travel time by 2-5x, eliminate traffic, and free up an hour of my day.  What if you could get from San Jose to San Francisco in 20 minutes, New York to Philadelphia in 30, and San Diego to LA in 35 minutes, it changes everything – both where people live and where they work.
  • Convenient & Ubiquitous: There is no travel time to get to your car: it’s right outside your house, or in the garage in your building.  Stations must with within a 2-3 minute walk, particularly considering weather (snow, rain, or sweating heat), packages (hauling groceries), and children.  Stations must be everywhere in an urban (or suburban) area that you need to go, not just the city center.  As a corollary, the system must be far less expensive to deploy and operate than today’s mass transit systems.
  • Self Routing:  Free up travel time for work or reading by having the vehicle “drive” itself, with no need for transfers, directions, knowing which streets only go one way, or which transit routes are most congested.  Type a destination, and the system finds the optimal path to your destination.
  • On-Demand: A vehicle is ready and waiting for you when you need it with little to no wait time.
  • Private or semi-private: Have your own space to work and converse, without being too bothered by other riders.
  • Safe: Eliminate traffic deaths.
  • Quiet & Nearly Invisible: So that people are happy to have the systems by their homes, with little to no auditory or visual disruption.

This is a tall order, and exactly what “Swift PRT Inc.” set out to accomplish.  As sailing vessels and steamships opened the world for exploration, and railroads opened up continents, a new form of transportation has the potential to fundamentally alter the world.  It’s also damn hard, but we’ll get to that in good time.

Swift Concept:

A magnetically levitated (maglev) personal rapid transit system seems the logical choice for the criteria above.  Maglev is fast and can have the quick acceleration and deceleration needed to reduce travel time over the short distances of urban and suburban areas.  It’s quiet.  In fact, there are no moving parts in the mechanical sense:  the vehicle is magnetically “floated” and then a series of magnets attract and repel the vehicle to give it momentum (a linear synchronous motor).  This theoretically should reduce operational costs:  there are no bearings to wear out, nothing to lubricate with oil; the suspension is in some sense much simpler than a car or train.

User Experience:

Users walk to small stations placed roughly 500 – 1000m apart where vehicle is waiting for them.  On a touch screen map, a destination is picked, and the vehicle automatically finds the fastest route given traffic, distances, and speed constraints.  Vehicles move at up to 200 km/hr, with rapid acceleration.  Combined with advanced traffic engineering algorithms, this can provide trip times 4-5x better than automobiles, before walk time to stations is included.


Vehicles are small, streamlined “pods” roughly 1.7m tall, 1.2m across, and 2.5 – 3.0m long.  The hold two people facing one another, plus plenty of storage behind the seat for groceries, bags, briefcases, etc.  Vehicles are light, weighing under 200kg, owing to the fact that they have no motor themselves, just seats, magnets, a touch screen computer, and two car-battery sized batteries.  Combined with passengers, this bounds the maximum vehicle + passenger to 500kg which is a crucial design decision.  Vehicles are connected to the track by two joints.  These joints bend, allowing the vehicle to bank with centripetal force around curves.


In order to fit into an urban area with no major changes to existing roads, buildings, or structures, the track is an elevated T-shaped guideway.  Each side of the “T” holds a different direction of traffic.


The system uses a permanent magnet to lift the weight of the vehicle, and continuous alteration of the magnetic field to stay a stable distance away from the track.  If the vehicle is attracted too close to the guideway, an electromagnet decreases the “power” of the permanent magnet, and the vehicle drops.  If the vehicle drops too far, the electromagnet adds power to the permanent magnet to pull the vehicle closer to the track[6].  Because the electromagnet is simply keeping the permanent magnet at a stable operating point, in the ideal case (no resistive loss, conserving charge with a switched capacitor design or perfect battery recharding) the electromagnet does no net work.

The system is propelled by a linear synchronous motor (LSM) attached under the track.  If the magnetic suspension fails, the system falls onto auxiliary wheels.  The diagram below shows the track as an I-beam to carry load, with the copper coils of the LSM attached below.  The magnets of the vehicle sit directly under the coils (not shown) and connect to the vehicle through the slot.  The auxiliary wheels ride on either side of the slot.


Vehicles exit the main track and descend to a ground level station.  The station itself is comprised of multiple vehicle bays.  Passenger enter the vehicle, close the door, hit their destination on a touch screen map, and the vehicle backs out a few meters, then ascends back up to the main track or does an ascending U-turn if traveling in the opposite direction.

The entire station is meant to fit within width of 4 meters, and have variable length.  In most places, this means the station is carved out of 2-3 existing on street parking spots, with a glass roof for weather protection, and a wall behind to protect the station from the road behind.  In other words, there is not much to each “station”; stations are just slightly larger than a typical covered sidewalk bus stop.

Key Decisions:

Having been exposed to the Swift concept, it’s important to understand why each key design decision was made to understand the tradeoffs.

Suspension:  Maglev vs. Wheels

Maglev was chosen for the suspension system as it is quiet – there are no motors, no wheels on pavement or wheels on track.  The only sound is the sound of pushing air.  This is very desirable in an urban area where you want ubiquity.  Maglev is quieter than cars, and far quieter than trains.

The system is also designed to be entirely computer operated, and have very little maintenance.  Wheels have bearings, treads, and lubrication that need periodic replacement.  Swift has wheels used only in power outage emergencies.

Finally, wheels impose an additional drag force that (at least in the case of steel wheels on steel track) scales linearly with velocity.

Guideway:  Elevated or Not

Ground-based transportation systems must compete for space with existing infrastructure: roads, trains, and pedestrian sidewalks.  Further, they suffer from the 2-dimensional intersection and queuing problem: whenever two roads cross, you need traffic lights, stop signs, or a round-about to prevent collisions on this shared resource.  This slows down transit time tremendously.

Restricted access highways solve this problem with under-passes and over-passes.  However, for a ground-based transportation system, such under-and-over passes are expensive to build, as they require moving many tons of earth to create ramps and artificial hills.

An elevated guideway solves the 2-dimension queuing problem, and if done in a lightweight way, makes under and overpasses much easier that in heavy ground transit.

Perhaps the most important reason to use an elevated guideway, however, is solving the “right-of-way” issue.  An elevated guideway with support columns only as thick as telephone poles and similar spacing does not need to buy large swaths of land; just tiny 50x50cm posts every so often.  This leaves the ground area free for roads, pedestrians, and existing infrastructure, with the future hope that as the need for roads is lessened, more of that land can be transformed into parks and outdoor space.

One deployment strategy is simply to replace existing telephone/power poles with the Swift structure, extending the support columns up further than the track to string power-line.  This gives Swift the rights of way needed for a municipality, and allows the municipality to modernize and improve a messy power-line / communications wiring infrastructure at the same time.

Vehicle Position:  Under or Over the Track

Most of us are used to vehicles sitting on top of a track.  After all, that’s the way cars and trains work.  This notion is likely so common it may not occur to most that there is another place to put the vehicle: under the track.

Swift’s maglev system works through attraction rather than repulsion, so the vehicle is actually pulled up towards the track.  While one could use a wrap-around design and keep the vehicle above the track, there are a number of reasons why, once we have decided to use an elevated guideway, vehicle below the track makes more sense.

First, it reduces the amount of track needed.  A vehicle above track or on a road must have a wide base, such that the center of mass does not tip the vehicle over laterally, particularly when cornering.  This means either a wide track, or two tracks in parallel for stability (like a train).  By placing the center of mass under the track, it can be supported stably from a single track.  This reduces expense and visual impact.

Second, vehicles can corner faster.  If we provide a hinge between the magnets and the vehicle, the vehicle with automatically bank on a turn with centripetal force at exactly the angle needed to keep the force of the turn down through the riders spine.  This avoids lateral jerk (and shoulder into the door) one gets when cornering too quickly in a car.

Third, by hanging underneath a track, the vehicle can approach the perfect streamlined body “teardrop” shape to reduce aerodynamic drag, something that is not possible when moving on top of the track where the bottom of the vehicle is roughly flat.

Lastly, it makes switching much easier, and faster.  In fact, no mechanical switching is needed at all – magnetic force pushes the vehicle over to the new track to complete the switch.

Weight & Riders Per Vehicle:

Weight is perhaps the biggest parameter we have to modify.  Most research and development for the past 150 years has been on trains or bus-like structures carrying 50 – 1500 people at once.  Such systems are heavy: the average locomotive weighs 100 – 250 tons, train car 67 tonnes[7], and even “light” rail cars weigh 45 tonnes[8].  Large systems require massive guideway structure, large columns, and are visually heavy.

By restricting the number of riders to a maximum of two people, we handle 90%+ of all travel (remember that the average car ride carries 1.2 people) and reduce weight to a minimum.  For groups of more than two people, vehicles can be routed together to arrive at the same time.  One could even use close circuit cameras to allow communication and conversation between vehicles.  This would be done with a combination of fiber optics along the track that are needed for control signals anyways, and periodic wireless installations.

Lower weight means smaller motors and cheaper power electronics.  To accelerate 500kg at a quick 3.0 m/s2 up to 200 km/hr requires a maximum 100kW (134hp) electric motor for each electrical block in the system ($2 – 3k in cost).  Smaller motors are inexpensive and can be mass-produced.

Lower weight means a flyweight guideway.  Carrying 500kg is trivial: concrete and steel have strengths above 100 kg/cm2, so support columns can be quite small.  Even small I-beams 10 cm in height have no trouble supporting 500kg.  The real issue is one of stiffness, as beams bend in the middle, and bending increases with the cube of the distance spanned between support columns.  Stiffness dictates that we will likely need to use a 30cm tall I-beam for spans less than 20m, and use a truss or cable-stayed structure for any spans over 20m.

What’s Different Now?

One of the questions I like to ask about any supposed innovation, or major improvement to an industry is: Why is this solvable now?  Why was it not solved in the past?  What has changed recently to make a new solution dramatically better than what existed in the past?

First is a materials innovation.  Neodymium magnets have the highest permanent magnetic field strength of any known material at up to 1.4 Teslas.  They were invented only in 1982 (by General Motors and Sumitomo Special Materials).  In contrast to permanent magnets, most existing maglev research in German and Japan is ultimately incremental improvements on 1960’s electro-dynamic technology.  Previously, it was assumed only electromagnets, generated on the track and on the train to repel one another, would be strong enough to produce a wide magnet gap for levitation.  If the magnetic gap is too small, deflections, oscillations, and installation imprecision could cause the vehicle to hit the track.  With strong permanent magnets doing essentially all the heavy lifting, the power consumption to do the actual levitation becomes nominal.

Second is fast embedded control system with precision electronics.  Earnshaw’s theorem says that two magnets attracting or repelling one another is inherently an instable system – you cannot put one magnet above another and expect it to float there indefinitely; the slightest perturbation and it falls off to the side.  One way to combat this instability is through an active control system.  For attractive maglev, this means the permanent magnets are wrapped in copper coil (an electromagnet).  If the permanent magnet gets too close to the track, current flows one way to decrease the net magnet field causing the magnet to drop.  If the magnet drops too far, the electro magnet switches current in the other direction so that the magnetic attraction is enhanced and is pulled closer to the track.  This process is done 100s or 1000s of times each second, a feat possible only with embedded computer systems.

Third is modern routing algorithms plus GPS.  It is now possible to keep track of tens of thousands of vehicles, positions, and velocities, ensure no collisions occur, and shape routes such that minimal traffic occurs and total travel time is minimized.  The later is one of Swift’s main areas of focus.

Energy Efficiency:

The two-person, under the track, lightweight, streamlined body vehicles of Swift provide a radical improvement over the energy efficiency of cars.  Whereas cars have a 15:1 vehicle weight to passenger weight, Swift is closer to 2:1 or less.  Further, aerodynamic drag force is ½rv2CdA, where r is the density of air, v is velocity, Cd is the drag coefficient determined by shape, and A is the cross sectional area.  Using a configuration where vehicles are 1.2m (one person wide) with passengers seating one another reduces the cross sectional area by a factor of 2x.  A drag coefficient of 0.10 is achievable, providing another 3x advantage over cars.  The net result would seem to be a 7.5 x 2 x 3 = 45x theoretical advantage.

At 100km/hr, a 3.0 m/s2 acceleration and deceleration, and accounting for things like on board power consumption, and electric motor efficiency, and regeneration of power during breaking, we can get efficiencies above 300 km/liter (800 mpg) on the 5km trip below.

  Total distance (m)


  Max speed (m / s)



km / hr
  Acceleration / Decel (m/s^2)


  LSM resistance (Ohm)


  Electronic power efficiency


  Pod + passenger weight (kg)


  Drag coefficient


  Fluid density


  Pod height (m)


  Pod width (m)


Area (m^2)


  Onboard power (W)







Time (s)





Distance (m)





Kinetic energy (J)






Aerodynamic drag loss (J)






Onboard energy (J)






Mechanical energy (J)





Average Force (N)





Average current




LSM I2R loss, (W)






Electronic transfer loss






Total energy input (J)






Average power (kW)






Liters of gasoline
Average power (hp)






km / liter
EI (Wh / passenger-km)








Table 1: Energy efficiency calculations.


In order to understand system dynamics, a simulator was created for network construction and test under a variety of traffic scenarios.

Network Construction Tool:

Built off of Google Maps, this system allows you to lay track out with reference to existing roads and buildings, then get immediate feedback on the velocity constraints imposed by network geometry.

An example network for the Stanford University and Palo Alto downtown area is shown below, as designed by a Google Maps based network-planning tool that has been created.  Color-coding shows the maximum velocity of the network based on centripetal force limitations imposed by cornering at intersections or curved/angled segments of track.

Routing Algorithm:

After using the map tool to layout an arbitrary network, the network is transformed into a formal directed graph structure, with edges being directional track, and vertices being stations or intersection points.

As many intersections occur at right angles, a critical parameter in the network simulation is the minimum radius of curvature at a right angle.  This was generally chosen to be around 5m, roughly the same as a car performing the same right angle turn on a street.  A larger radius would only be possible in areas without nearby buildings, and one of our guiding principles is that little to no existing infrastructure should be altered to put this new transportation system in.

The radius of curvature between three clockwise or counter-clockwise line segments can be calculated using the middle segment as a tangent curve.  All other curvatures can be found through an atan2 scaling of the right angle radius as the “smoothing” algorithm.

The system then calculates the all-pairs shortest path (in time) using these geometric restrictions.  This is the best possible no-traffic time from source to destination, using maximum acceleration until either maximum system velocity is reached, or maximum deceleration is needed.

Handling traffic is a very difficult problem.  It is tempting to cast this as a multi-commodity flow problem.  Unfortunately, that’s difficult for two reasons.  First, the multi-commodity flow problem with integer values (if we consider each vehicle as a separate commodity being sourced from the origin, and demanded by the destination, then all flows are the integer 1) is NP-hard.  There is no known algorithm that will always produce an optimal solution in bounded time.  Second, flow, such as in a data network like routing internet packets or time-division mobile data, is continuous, whereas vehicles are discrete: we are routing only “1 bit” one time.

While it is tempting to use purely congestion metrics (e.g. this track is 90% full, so avoid going there), this approach is also incorrect.  Even if a link is mostly full, if my vehicle arrives at exactly the right empty time slot, the link “appears” empty to me, and I can move at maximum speed.

What is needed is a time-slot finding algorithm, where a “time-slot” is that empty space (or equivalently span of time) between two other vehicles that this vehicle slides into.  Put another way, it’s finding the “gaps” to merge into on each road being traversed.

The time-slot finding algorithm developed starts at the source, carrying with it some time “slack”.  Time slack provides a window that says: “If needed, I can leave anytime between now and say 1500 milliseconds from now”, for example.  The vehicle attempts first to follow the optimal no-traffic route in time, along with the velocity profile of maximum acceleration and deceleration needed to minimize time.

At the input to each edge, slack is used to look at which open time slots could be made between [arrival time, arrival time + accumulated slack).  That is, slack can be used to slow down from the optimal speed in order to slide into an available time slot if needed.  At each link, additional slack is accumulated, such that the total slack is bounded to a threshold value, say 10%.  A 10% threshold means that vehicle routing can be up to 10% slower than the optimal no-traffic time, if needed to weave through open time-slots and find a viable source to destination timing.

The process continues recursively on the tree defined by empty time slots.  If a time slot can be found on every link from source to destination, it is claimed for the vehicle in a central database with a lazy locking mechanism.

If no successful timing can be found, the most congested links are removed from the network search, and a shortest path algorithm (the A* algorithm) is run on the remaining graph structure to find an alternative route.  In this way, we route around congested links, even if they happen to be on our ideal shortest time route; traffic has made them too costly.

The time-slot finding algorithm is similar to a greedy, bin-packing algorithm (packing time-slots together is the equivalent of packing bins) where each vehicle takes it’s own shortest possible timing.

Many heuristics can be created for when and where to take slack timing.  One strategy, for example, is to take slack (which always occurs by slowing down) on those links that are least congested, or furthest away from a known, frequently congested route.  This prevents the congestion from “spreading”; if we slowed down on the congested link, or those links leading to the choke point, then subsequently routed fast moving vehicles would have to place a large time buffer between themselves and our slow vehicle to avoid collision.  By taking slack elsewhere, velocities mismatches are minimized on busy links, leading to smaller time buffer requirements, leading to denser vehicle packing, leading to higher throughput on the congested link.  Another way to look at this is as an evening out algorithm: vehicles entering a congested area are let in at a measured pace and near perfect velocity.


Traffic can be generated at each station either randomly, or from the population served by that station (inferred from the population density of the zipcode, and then an n-minute walking radius out from the station).  Traffic density can either be varied by time of day (rush-hour), or spiked until the entire network saturates.


Using the simulator, plus an 18-station 25km mesh test-network covering the Stanford University / Palo Alto downtown area, sensitivity analysis can be done on a number of parameters.  For all scenarios, a large number of vehicle requests were made within a short time period to fully saturate the network and test it’s limits (precisely, 1000 requests from each station randomly but even distributed over a 200 second window).


Default Value

Max acceleration / deceleration 3.0 m/s2
Max system velocity 60 m/s
(216 km/hr, 134 mph)
Centripetal force limit 0.25 Gees
Maximum slack 10% of trip time
Right turn radius 5 m
Minimum vehicle spacing 10 m

Table 2: Default simulation parameters.

Max acceleration and deceleration were chosen such that with a 500kg vehicle plus passenger payload, total power would never exceed 100kW.

Government standards for people movers in a seated configuration specify a maximum lateral force of 0.25 g.  This is conservative, in my opinion, particularly for a system that banks optimally (since the hinged vehicle swings out while going around corners) and therefore puts the force straight through the spine/seat of the rider.

The base result is:

Network capacity 39,762 / hr
Avg. velocity over all routes 21.44 m/s
Max single route velocity 35.45 m/s
Average vehicle spacing 3.7 s
Min. single link vehicle spacing 1.9 s


Google Maps indicates drive time between the two furthest stations as 12 minutes.  Simulated time between those two stations never exceeds 200 seconds, indicating a 3.6x speed advantage over driving.

While the system allows a velocity up to 60 m/s (and vehicles hit this maximum for short stretches on long straight-aways), the average velocity accounting for acceleration, deceleration, cornering and centripetal force limits around curves is much less.

Average vehicle spacing is 3.7 seconds.  This number is higher than expected for two reasons: vehicles going around right-angle corners must slow down to a centripetal limit of v2/r = 0.25g, or 3.5 m/s (12.6 km/hr, 7.7 mph).  This forces fast moving vehicles behind them not to slow down, but to create an up to 10-second time buffer to prevent overrunning the slower vehicle.  The second reason is vehicle requests come in randomly (i.e. riders start their journey at an arbitrary time).  This means the time slots claimed by their vehicles are randomly dispersed.  Instead of time slots being perfectly packed, small fragmented time-slots too small to fit another vehicle appear.  This could be somewhat alleviated on busy links through an alignment procedure (like the timing stop-lights used for entry onto a freeway), however, this option can simply push the congestion to another location in the network.

Network capacity tops out at around 2200 vehicles per hour per station (there are 18 stations in the test network).

Upping the centripetal limit to 0.50 g, and allowing for more gradual curves by pushing the right-angle radius to 50m gives:

Network capacity 45,003 / hr
Avg. velocity over all routes 28.95 m/s
Max single route velocity 42.37 m/s
Average vehicle spacing 2.8 s
Min. single link vehicle spacing 1.7 s


We see a 14% increase in network capacity, a 24% improvement in vehicle spacing, and a 35% greater average velocity.  Of course, a 50m radius of curvature is likely impossible in urban and suburban areas where buildings near street corners likely prevent such lazy turns.

This shows the power of the simulator in optimizing and trading off any parameters from power consumption to trip time to velocity to rider comfort (based on G-forces experienced).

Fundamental Limitations:

Turns at an intersection:

Radius of curvature actually turns out to be one of the fundamental limitations in a high-speed terrestrial network (regardless of maglev or not).  Centripetal acceleration is v2/r, where v is velocity and r is the radius of curvature.  With r = 5m, we are limited to 18 km/hr at 0.5g.  Even at a radius of 50m, such as the long on and off ramps of interstate highways, our maximum speed is 56 km/hr (34 mph).  Thus, curves dramatically affect our top speed and trip time.

Single-lane road problem:

Turning at an intersection, or slowing to descend to a station, has a major impact on system capacity.  A buffer of up to 10-seconds (depending on max deceleration and max system velocity) must be put in between a very fast vehicle, and one slowing down to corner.

Instead of the naïve capacity calculation of 10m spacing, 60 m/s max velocity = 21,600 vehicles / hour, we have 1/10th that value in actuality.  And because mass transit systems (subways & heavy rail) can carry 10-20k people per link per hour, a personal rapid transit system like Swift can never compete on single-link capacity.  In fact, the capacity of a highway is roughly 2000 vehicles per lane per hour, meaning PRT is as good as a lane of interstate highway, but likely no better.

I call this problem the “single-lane-road” problem.  For any track-based system, you effectively have a single-lane highway; no passing is allowed, and if the vehicle in front slows down, you have to slow down (or put a large enough time buffer that slowing down is not needed).  The way around this is to do what highways do: have long on (off)-ramps that can be exited (entered) at near maximum system speed, so there is no velocity mismatch with the vehicles in the “fast lane”.  The problem with that scenario is at 3.0 m/s2 acceleration, and 60 m/s maximum velocity, it takes 600m to get up to maximum speed (and another 600m to decelerate to zero).  If your intersection or station spacing is meant to be <1km apart, you effectively have need two lane in each direction: fast lane, and an acceleration/deceleration lane.  The net result is you have at least doubled your track costs, and the width of your system.

Acceleration Limits:

The logical way to prevent needing two-lanes at all times might be to allow better than 3.0 m/s2 acceleration and deceleration, so that the time needed to get to a maximum speed is lessened.  At 1 Gee, four times the suggested regulatory limits, acceleration to 60m/s still takes nearly 200m.

Regardless of implementation (maglev or wheel based, elevated guideway or ground level), the grid-like structure of urban and suburban areas fundamentally limits travel times for terrestrial transportation.  With centripetal and acceleration safety limits of about 0.5g, and many right-angle turns required (unless buildings are removed or track literally cuts through the buildings), we are forever physics constrained to a system average below 100 km/hr (60mph) for short trips of <5km.

Construction Economics:

Now that the simulator has given us a good feel for systems level behavior (capacity, traffic, average velocities), it’s important to look at the economics of building such a system.

Elevated Guideway:

After consulting with a couple of structural engineers who in turn talked to a number of builders, it is believed that a simple T-shaped elevated track structure for carrying both directions of track with vehicle + passenger limited to 500kg, could be built for $4m per kilometer, with 25% cost in support columns, and 75% in the track beams and trusses.  Of the $4m cost, roughly $2m is in material and $2m is in labor.  This is similar in cost to ski-lift systems, where cost runs around $2 – 3m per kilometer[9].


Underneath the I-beam support structure are the copper coils, iron laminations, and wiring needed for the linear synchronous motor.  While the initial assumption was the linear synchronous motor (LSM) would scale down with weight, the key parameter is force per unit length, as this sets the maximum currents through the LSM, and therefore the size of electro-magnet needed.  On large systems, this force is often distributed over the length of the entire train car, whereas in Swift, it is contained within just 2 meters.  In either case, the force per unit length, and the work done by an individual coil is about the same.  This results in an LSM where the

cost of raw metals alone is around $400/m (half copper coils & cabling, half steel, bolts, and attachment systems), with the installed cost likely being $1000/m.  Since we are looking at a system with two tracks (one going in each direction), this adds $2m / km.


By reducing the weight and keeping acceleration at 3.0 m/s2, vehicles need a peak power of 100kW, and this sets the size of the variable voltage, variable frequency electric motors needed to propel the vehicle.  Electrical block spacing is assumed to be 10m, which also defines how close two vehicles can be (only one vehicle per active electrical block).

At $2000 per electrical motor, we have 2 directions * 1000 m / 10 m spacing = $400,000 in electrical motors for the bidirectional track per kilometer.  Add $100k for wiring and power conditioning, and we have $0.5m per kilometer.

It total the cost per kilometer before stations and vehicles could be as low as $7m per kilometer.  Adding a simple station, 20 vehicles per kilometer at $20k each, and amortizing the cost of a maintenance building every 10-20 stations, we take the total cost per kilometer optimistically to be around $8m.

Cost per Population:

In addition to the “empirical” studies done using a simulator, it’s important to calculate the cost to serve a particular population.

Dense Suburbia:

Let’s take downtown Palo Alto, California as an example.  Downtown Palo Alto has a population of around 15,000 people, living in about three square miles (5000 people/mi2, or 2000 people/km2).  I consider this to be “dense suburbia” with plenty of apartment complexes and townhouses and single-family homes typically on less than 0.25 acres.

To put a station within 3 minutes walk, we need about 10 stations serving the area.  Capacity is not an issue: even if the entire population traveled on any given day, a single station would be sufficient.  In fact, it is likely that no single station would peak at more than 200-300 riders per hour (one leaving every 12 seconds) even in the worst case.

To cover the area with this number of stations takes at least 15km of track.  Track can be reduced to 8km using a minimum spanning tree instead of a mesh network, but then travel between two seemingly close stations must travel up the “tree” for a while, before coming back to the other station.  At $8m / km, 15km of track would cost about $120m, or $8000 per person in the population served.

To make a point of comparison, the State of California spends about $320 per person on transportation infrastructure (with potentially more federal funding coming in for major highways)[10].  That means blanketing the area with Swift track in a way that is ubiquitous enough to actually replace or greatly augment the use of cars would take 25 years worth of transportation spending.  Cost should be <$1,000 per person to have a chance at economic success.

Dense Urban Area:

If dense suburbia does not work, let’s try the densest urban area in the United States:  New York City.  Assume we are trying to replace the subway system with Swift.  The subway provides 5.2m rides each weekday, peaking just below an estimated 1.0m rides / hour during morning rush hour.  Assume that the average journey takes only 10 minutes (2-4x faster than even the express subways).  It takes another 10 minutes to route the empty vehicle back out to where it’s demanded, for a total vehicle time per person (assuming single rider per vehicle) of 20 minutes.  To handle peak rush hour then, we need 333k vehicles.

If it takes 30 seconds to enter a vehicle and type a destination, and each station can handle 2000 vehicles per hour, then we need 18 vehicle bays to keep the throughput maximized, and 1.0m peak people / hour divided by 2000 people per station per hour = 500 stations to accommodate them.  The subway has 468 stations in New York, so 500 stations (even if our rough estimate is off by a factor of two) is not prohibitive.  Nor is the number of vehicle bays per station.  Vehicles are small, and parked diagonally, can be spaced 2-3m apart.  Subway trains can be up to 180m long, enough space for 60+ Swift vehicles.  Things are looking good.

The real problem with PRT in dense urban areas is parking.  During non-rush hour periods, what do you do with 333k vehicles?  While one vehicle for every 8 commuters is far better than can be done with cars, 500 stations by 18 bays means parking only for ~10k vehicles.  The remaining 323k vehicles at 3m long would require at least 1000 km of extra track (perhaps an $8b cost for parking alone).  This compares to a rolling stock of only 6600 subway cars to handle the same traffic, a 50:1 ratio.  Parking is a major problem for PRT.

Density Requirements for PRT:

Leaving aside the parking problem, at what population density would PRT make sense?  If we have restrict cost to $1000 per person in the population being served, have a cost of $8m per kilometer, and assume that we use a total track of twice that station spacing length for each station (i.e. halfway between a minimum spanning tree and a full Manhattan grid mesh), we can calculate station spacing and average walk-times for the population being served:


Density (pp/km^2)

Station Spacing (km)

Avg. Walk Time (minutes)





New York




San Francisco








Dense Suburban








Table 3: Station spacing & average walking time to stations by population density.

Future of Transportation:  Not PRT or Light-Rail

To replace the convenience and door-to-door speed of cars with a new form of transportation, we need a combination of speed, ubiquitous access, on-demand departure, quiet, privacy, and safety.

At perhaps $8m per kilometer (or even potentially as low as $5m per kilometer), the ultra lightweight, elevated maglev guideway of Swift can compete with the cost of interstate highways ($4 – 10m per lane per mile).  However, it cannot compete with the ubiquity of smaller streets and highways who’s cost per kilometer can be $100 – 300k.  It’s hard to beat asphaltic concrete at $17 / tonne versus $900 for steel (53x) and $10k for copper (590x).

Personal Rapid Transit and Light Rail systems simply cannot put enough stations in even dense suburban areas to beat the automobiles.  While travel time once at a station and going to another station can be up to 2x faster than cars in light-rail, or 4x faster for Swift, this improvement is killed by walk time to and from stations.

If stations are spaced 2.6 km apart, this adds an average of 8.5 min of walk time to a station.  If the walk time is the same from a station, that’s 17 extra minutes per journey.  Let’s assume that your average driving speed is 72 km/hr (45 mph), and Swift provides a 3x speed advantage (216 km/hr or 135 mph).  For any distance less than 27km (17 miles, or 23 minutes of drive time) in one direction, it’s still faster to drive.  Even halving trip times is possible only in a handful of terrible traffic locations (Los Angeles, Washington DC and New York), where commutes average 45+ minutes each way.

The real cost of transportation is mathematical:
Real Cost Public Transit = Fare + Salary(Time to station + Time from station to destination + Transit time + Wait time for train)
Real Cost Auto = Distance * Cost Per Km + Parking Cost + Salary(Time to park + Transit time)
These equations cross in favor of public transit only when stations are ubiquitous (<5 minute walk away) and the wait time for a vehicle/train is nominal, or the cost of auto transit goes up 3-4x it’s current $0.21 / km.  Otherwise, it’s cheaper to drive.

Station ubiquity in turn is only economical for regions that have population density above about 5,000 people per square kilometer.  This may be why taxpayers, rather than riders pay 90% of the costs for light-rail systems, which are typically deployed in low-density urban areas.  Across all light-rail systems, cost per passenger mile runs about $1.20 versus $0.34 for a car[11].  Add in the time factor to get to a station, and the real cost of public transit outside dense urban areas is much worse.

Future of Transportation:  Self-Driving Cars

We live in a world designed around cars.  Because world population has grown five-fold during the age of cars, we will be stuck with their legacy in roads and low-density metro configurations for at least the next century.  This realization is a difficult one – I set out to start a company that could radically transform transportation.  But neither the physics nor economics work out, and in fact will not work out until population density is much higher[12].

It is the ubiquity of roads, more than the greatness of cars that is difficult to defeat.  And so, the future of transportation is, perhaps disappointingly, simply better cars.  Our abstract criterion for the perfect transportation system is one that is fast, ubiquitous, has on-demand departure, and is quiet, private, and safe.  The solution to all of these is a self-driving car.

In a test done back in 1997 with normal vehicles (Buick LeSabres) whose throttle and breaking was put under computer control, a group of vehicles was “platooned” together in groups of 10 with car-to-car radio controls.  Spacing of just a few meters could safely be established, with automated merger to the back of the platoon, and exiting the platoon for departure[13].

Such systems would allow highways to go from 2000 vehicles per lane per hour to 4000 or more, effectively doubling the capacity of highways.  In a platoon configuration, air resistance is cut by up to 35% (with corresponding improvements in fuel efficiency).  If the cars were electric, quieter operation could be realized.

The future is a self-driving, tight-following vehicle that routes itself according to traffic patterns to minimize total drive time across all travelers, that parks itself, or returns like a taxi to pick up its next passenger.  The last point is particularly salient: self-driving cars can be like taxis – you don’t need to own the vehicle, there simply needs to be one that can pick you up at a moment’s notice.

Next Steps for Swift:

It is clear that a maglev based personal rapid transit elevated track system should not be pursued as a business.  The routing and traffic contention algorithms, however, are likely the same system-level optimization algorithms needed for self-driving cars.

If anyone has plans to create a device that can plug into the cruise control or computer system of any late model vehicle to provide driverless operation (perhaps Google’s Self-Driving Car will license or open-source their vision system), do traffic routing from a central traffic database, and do car-to-car wireless signaling, let me know (apatzer (at)  This is something I’d like to fund, participate in, or engineer.

Until then, it’s back to the drawing board with a next venture.  At three months of research, and three months of non-stopping coding, this was a fast failure, and worthwhile fun.


[1] “Public Transportation: A Bad Product at a Bad Price”, John Semmens, Heritage  Foundation.

[3] U.S. Census Bureau’s American Community Survey

[4] Clark County Wisconsin, “All Season Road Construction”,

[5] Washington State DOT, “Highway Construction Cost Comparison Survey”

[6] The best maglev suspension systems in my opinion are those from Magnemotion, as described in “The M3 Urban Transportation System. Part of FTA Project MA-26-7077”,

[8] Siemens P2000

[9] Peruvian Express Construction Costs @ Snowbird,

[10] Caltran budget for 2010: About $8B ($270 /pp) on new outlays each year, and $1.5B in maintenance ($50 /pp).

[12] Or the cost of raw materials is much lower (which would likely only be possible with a massive reduction in energy costs – half the cost of steel, for example, is the energy required to smelt it).

[13] “Vehicle Platooning and Automated Highways”,


  1. Andrew J Scott
    December 4, 2011

    Would the algorithms be applicable (and might the result be different in terms of commercial feasibility) if applied to a long distance scenario; specifically I’m thinking the UK’s HS2 (High Speed 2) rail, for which I don’t think a maglev has truly seriously been considered.

    It is frustrating to me that a project which will take millions and ten years to complete, will be the implementation of what is nearing the epitome of a 150 year old technology (i.e. traditional rail), rather than the deployment of an advance in an -already proven- technology (maglev) which would stand the UK in good stead for future generations and potentially deliver a game-changing increase if speed of travel.

    Such a substantial decrease in journey time might genuinely catalyse social change or economic improvement, rather than otherwise only a marginal improvement in UK’s North/South public transport infrastructure; I suspect in addition many of the base costs (land purchase, labour, re-routing of existing roads, power deployment and landscaping) remain similar for high speed rail or maglev.

    This report makes for a fascinating read and is yet another demonstration of how rapid iteration and fast failure analysis can provide the rational (or not) to proceed with a venture.

    A government funded analysis would I’m sure have taken years and millions in cost.

    • apatzer
      December 4, 2011

      Andrew, for high-speed rail, most maglev today uses a variant of the German Transrapid technology invented in the 1960′s. Because it’s an electrodynamic system where levitation requires creating an electromagnet on the track and on the train, it takes quite a bit of power, and can cost $100m+ USD per kilometer. A better approach for the longer distances you’re talking about is the maglev technology from outside of Boston. They’ve been around for about 15 years, and have by far the best suspension technology for maglev, and at a much cheaper price point.

  2. Rokhayakebe
    December 4, 2011

    What about a KivaSystems-like system?

    • apatzer
      December 4, 2011

      I don’t see how that’s applicable for high-speed transportation. Their system is fine at warehouse logistics, but doesn’t solve a transportation problem. Variants of those algorithms might be usable for a systems-level control of self-driving cars however.

  3. Tim
    December 4, 2011

    This appears to be very similar to the SkyTran concept. See

    They came up with solutions to some of the problems you found. They used a version of passive maglev that is less costly and complex than the active maglev that you are proposing. See

    Inductrack uses passive coils or possibly laminated aluminum foil disks on the track.
    Magnets on the car induce a current in the coils on the track. This makes the track a lot cheaper.

    As for the speed problem in cities, you could have one or more high speed north-south routes that have have off ramps that decelerate the cars to that they can go on slower east-west routes that can have turns in them.

    • apatzer
      December 4, 2011

      I’ve met with the SkyTran people. In my opinion it’s a sham that’s gone no where in the 15 years they’ve been advocating for it. If you look at their website, they claim things like runs on the power of two hairdryers (let’s say 3kW). Obviously they’ve never done even the basic energy calculations – you burn far more than that in aerodynamic drag at even automobile (100km/hr) speeds, even if you have a perfect drag coefficient (0.06 for a streamlined body), and a cross sectional area of less than 1m^2. They also claim capacities equivalent to 3 lanes of highway. Ridiculous to anyone who’s built a true physics based simulator (as I did with Swift). You could theoretically pack vehicles that tightly, but at a minimum you would need two lanes (a fast lane, and an acceleration/deceleration lane) to pack the fast lane that full. I go through the full calculations in the “Single Lane Road” section under “Fundamental Limitations”. SkyTran is not rigorous or real.

  4. Shae Erisson
    December 4, 2011

    What about using passive maglev such as Inductrack and building in areas that do have higher than 5000 ppl/km2 ? New York has twice that density.

    Also, you’ve left out the benefit that each person gets more “non-working” time in mass transit.
    I rode the subway in Stockholm more than an hour each day, but I used that time to read and communicate, I did not have to pay attention to driving.

    Thanks for the quantified numbers here, I shall spend more time examining this!

    • apatzer
      December 4, 2011

      I started out my research by reading every paper ever written on Inductrack, and met with Dr. Post and his colleagues at LLNL as part of my diligence. The major problem with Inductrak as a “passive” system is that you have a magnetic drag spike that takes about 4x normal power to initially overcome. Since the size of your electric motors is set by your peak power rather than your average power, you need motors 4x bigger (and at least 4x more expensive) than you “actually need”. Inductrack also requires a linear synchronous motor (LSM), which is the major cost component. The actual permanent magnet suspension (which is what Swift advocates, just the Magnemotin version vs. the LLNL Inductrack version) cost is negligible.

  5. AmirS2
    December 4, 2011

    So if parking is a problem, and travel time to stations is a constraint, how about having hybrid pods, that also have wheels and electric motors so they can drive on roads. They could be privately owned and parked in your driveway or rentable and drive round to your house to pick you up automatically. They would only need enough battery to get from your home to the nearest ‘on-ramp’ station to get onto the track network. They could use regular car parking facilities at their destination.

    Does this change the economics enough? It should require much less stations and double track, but would add to the cost / complexity / weight of the pods, although I’m thinking just enough electric wheels/motors to do say 20-30 km/h in a suburban setting, so hopefully not too much extra cost.

    • apatzer
      December 4, 2011

      Amir, I’ve thought about using a hybrid idea where the “pods” can themselves also drive on roads. First, this does nothing to reduce the cost of the track needed to cover an area, second, the big advantage Swift has are lightweight vehicles (200kg) such that vehicle + passengers < 500kg. The vehicles themselves don’t have motors…the linear synchronous motor on the track provides the propulsion. Adding a motor, plus wheeled suspension, plus the safety equipment needed for on the road travel adds 1000kg to the vehicle, making them much heavier to suspend, larger in dimension, and less aerodynamic.

      • Vadim Lebedev
        December 5, 2011


        Sure the autonomous pod perturbes the scheme however did you consider
        a system where the pods are not really autonomous but have a possibility to land on autonomous chassis for passengers not willing to have 8.5 min walk (actually i suspect that it will be a small minority of passengers).
        The chassis will need to have max speed around 30 km/h and range of 2-3 km which
        means no big batteries which could be relatively rapidly recharged.

        Btw your math for transit duration seems to be overly optimistic by not taking into account traffic jams.

        • apatzer
          December 5, 2011

          Vadim, Swift vehicles have no motor per se, the linear synchronous motor that drives them is built into the track. To allow them to be driven on a road on the way to a station requires adding a motor, increasing the size of the vehicle for lateral stability, and adding safety systems (for crashes). All of this adds tremendously to the weight. The big advantage of Swift is the vehicle weighs only 200kg, which with passengers means maximum load is always <500kg. Adding car components increases this tremendously. Further, to get the “cars” to people, you would need far more vehicles – likely the same as cars today – as they would remain parked at people’s houses.

          • Vadim Lebedev
            December 8, 2011

            It seems that i didn’t make myself clear….
            My idea is to keep your vehicle as it is… So while it is on rail nothing changes with respect to masse and autonomy.
            But when it arrives to the destination station it can land on an autonomous wheeled platform which will have a range of 5-10 km to drive to final destination and then bring your vehicle back to the rail station.
            This way the people not willing to take 10 min walk will be able to choose to be ‘delivered’ to the final destination (or picked up at home).
            So with respect to the rail noting changes (well actually i think with this setup the stations could be more spaced that in in your original scheme).

  6. Nicholas de Wolff
    December 4, 2011

    Fascinating and impressive research and analysis. Your work will prove invaluable in assessment of options available within this transportation sector (still “alternative” after all these years, even though variations have been proposed, and even implemented since the 19th century. One interesting local variation here: – though note that the absence of *combined* governmental and local business support served to kill the project, in much the same way as so many emerging transportation and urban design initiatives are terminated today:

    Point being that your challenge is at the very least parallel on two tracks (if you’ll forgive the pun!): developing the algorithmic and geographic models necessary to validate the concept is one part of the core equation, for sure. Realizing a tactical process that will successfully manifest the plan in the “real world” is an altogether different proposition, unless you are Google (Ultra High-Speed Fiber project:, and have the moolah to implement with 100% private funding and minimal controversial geopolitical impact.

    I wish you nothing but success in this very worthy venture, but my own experience as a government consultant on transportation and urban design, has shown that all the logic and good sense in the world will often not suffice to overcome political intransigence. Prove me wrong, please!

  7. John Carpinelli
    December 4, 2011

    Tethered electric aviation can meet all of your requirements for a future transportation system:

    Fast – air travel is faster for long trips. With an efficient takeoff and landing system, it can be faster for suburban journeys also.

    Quiet & Invisible- silent takeoff using winches and cables. Google “electric takeoff” to see the concept.

    Convenient – Take-off/Landing zones could be deployed on top of buildings and parking structures in every neighborhood.

    Safe – Air transport is very safe and already deploys autopilot systems.

    On-demand – Air taxi service is ideal for point-to-point travel for individual groups.

    Private – Small aircraft for 2-4 passengers are in common use already.

    Nearly Invisible – Air traffic is generally out of sight for people on the ground. Once the noise is eliminated with tethers and electric propulsion, our cities will be much more peaceful.

    Electric aviation can deliver transport cheaper than diesel trucks, buses or automobiles. Land use is a fundamental problem for efficient transport, and aviation avoids the massive costs of building out ground infrastructure. See my web-site for details. We are building flying prototypes now and we need people to develop the concept further.

    • apatzer
      December 4, 2011

      John, that system is interesting. So essentially, you have an aircraft flying circles around the airport towing a “power cable” behind it, then to take off, aircraft have a flexible harness that links to the power cable sort of like how electric cable cars and light-rail munis touch a power rail above them with a flexible connector?

      • John Carpinelli
        December 4, 2011


        There is no electric power transfer to the payload like light-rail. The tow aircraft is powered by electricity from the grid and flies in a circle tethered to a rotating hub on the ground. There are electric winches mounted on the rotating hub. Payload aircraft are winched to altitude using a second pair of cables attached to a pulley beneath the tow aircraft. Note that the hub is turning slowly at one revolution per minute so that payload can attached on the ground. As the payload climbs, it accelerates to the tow aircraft velocity also.

        The payload aircraft uses no fuel or propulsion for takeoff and then flies a gliding descent towards the destination. Some battery power can be used for landing and reserve power. There are alternatives that use tethers for a silent vertical landing also. The history section of the site links to some variants on the idea.


  8. Broadcastic
    December 4, 2011

    My friend has several MAGLEV patents and his estimation is $7.5M per mile track cost, about $3.5M of that is just cement. but this one is for full blown MAGLEV, for personal we’d probably can do $5M per mile.
    I’d love to participate in the project. Where do I sign up?

  9. Will
    December 5, 2011

    This entire analysis lacks the most basics elements of critical thinking. Really? “The real problem with PRT in dense urban areas is parking. During non-rush hour periods, what do you do with 333k vehicles?”

    When did every single person in NY go out and buy cars so they can drive them three blocks to the nearest PRT station to park?

    That is a huge face-palm.

    The rest of your reasoning is similarly silly:

    In your Palo Alto example you get to $8000/person compared to $320 CA spends. However:
    - I still need to pay $x for my car, where PRT may replace that need ( a huge number of people in NY / Tokyo don’t own cars )
    - What is the fare for PRT? subways aren’t free either. This revenue goes into determining what the real cost / person is.
    - It’s rather obvious PRT isn’t suited for Palo Alto. There is hardly even traffic with cars.

    In your NY example:
    - You assume you need to “route the empty vehicle back out to where it’s demanded” , doubling the travel time.
    - The subway still exists, you don’t need to cover the total demand
    - A subway and a PRT are fundamentally different: the subway ride isn’t point-to-point and may require several changes. It’s big and dumb. I’d happily pay $20 to get a 20 minute, quiet, point-to-point ride from Queens to Wallstreet.
    - Some retardation about needing parking structures

    • apatzer
      December 5, 2011

      Will, I think you’re missing the point. When I say the real problem with PRT in dense urban areas is parking, I don’t means parking cars at PRT stations, I mean parking the PRT vehicles (Swift pods) themselves. My NYC example was a thought-experiment on whether the system could handle the same capacity as the subway.

      • Andrew F
        December 9, 2011

        Parking of excess vehicles is a trivial problem, much like your concern about speed in curves. You just add some sidings. For turns, you add turn lanes to allow for deceleration/acceleration. To store vehicles, you add a hundred meters of siding in a few strategically location locations. The cost of this is insignificant on the system scale.

  10. Max
    December 5, 2011


    Please be sure to check out this technology instead:

  11. Jim
    December 5, 2011

    I dont know about most people, but a Swift system would be a wonderful replacement to the current commuter trains to/from downtown Chicago and it’s suburbs. Even if it’s never used to replace cars, it would make commuting oowntown much faster and easier. The savings in fuel alone for trains would be amazing, considering how much is wasted trying to start and stop a 67 ton vehicle.

    In fact, such a system would make commuting farther much more possible. I could see commuting 80 miles away if it means taking a 200 mph 2 person maglev car that didn’t have to make stops every 3 minutes.

  12. Gary Wheeler
    December 5, 2011

    As any architect knows, the problem is handicapped access. How do you get a wheelchair and an attendent person (or animal) into the vehicle.

    Your concept reminds me a little of the cable supported vehicles used in bananna plantations… but in a good way. :-)

    • apatzer
      December 5, 2011

      Handicap access is easy. Some small number of vehicles have the two seats removed, thereby creating enough space for a wheelchair. The vehicle is 1.2m wide, and 1.7m tall, which should accommodate a wheelchair just fine.

  13. Mark
    December 5, 2011

    One aspect I couldn’t find in your cost calculation is the value of reclaimed land made available for other uses by the reduced need for on-site automobile parking. The additional revenue resulting from the transformation of unproductive asphalted expanses to productive businesses and housing would, I think, be quite significant.

    • apatzer
      December 5, 2011

      Mark, that’s true, and it you calculate reclaimed land, then the system cost here would arguably decrease such that it would be competitive with asphalt roads. The problem is, how do you get there in the intermediate time frame when you have Swift and roads coexist? Also, Swift does not eliminate the need for roads entirely. You still need single lane roads for heavy deliveries (Swift’s payload limit will not let you transport a large couch or steel I-beams for example). The land reclaimed is in reducing a 4-lane street down to 1-2 lanes, which is still significant. With Swift everywhere, the landscape would look much more like a college campus, where you have access roads used only for deliveries and maintenance, and not the concrete jungle we have today.

  14. zxc
    December 5, 2011

    If the pod could tilt forwards/backwards as well the acceleration/deceleration would not be felt by passengers as much. Also having the track go higher at curves would allow slightly higher deceleration before a curve and acceleration after a curve without requiring more power.

    • apatzer
      December 5, 2011

      While that suggestion sounds good, power is not a limitation during deceleration (power is negative, as in, deceleration puts electricity back onto the grid, and aerodynamic drag force decreases as you decelerate). The limitation is the deceleration in G-force felt by the passenger. Simply having the track go higher around a corner might lessen the power output of the motor, but the effective deceleration rate is still constrained by the stopping force you can reasonably put on passengers (particularly elderly and children).

      • fgouget
        December 10, 2011

        > power is not a limitation during deceleration

        Yes it most likely is. The deceleration is limited by the force that your engine can apply which is a function of its rated power. So the same factor that limits acceleration limits deceleration. All you gain is aerodynamic drag. The ability of the grid to provide or absorb power is probably not the limiting factor here.

  15. userulluipeste
    December 5, 2011

    You criticize the current system in which cars dominate, with public transport dropping from 50% to 2%, but that happened with a reason, you know? No public transportation system will offer a real alternative to privately owned transport. Exclusive access to something IS IMPORTANT. Hygiene is only one example that can be deduced from that. Different people have different requirements, and the current system is accommodating them all. You and others like you are calling for leveling out all these differences, something very much alike to what the communism wanted – leveling out everything. You, as many deluded idealists are calling for something, without considering important real factors.

  16. Nick
    December 5, 2011

    Hi Aaron,

    Really interesting bit of concept development. I agree on your conclusions regarding the dominance of self driving cars on existing roads as the future of urban transport. I went a way down a similar path a couple of years back (electric low emission vehicles, all the usual suspects as motivation, aim of light weight etc) but abandoned it once it became clear that larger OEM’s were already moving in that direction (for e.g. the fully electric Renault Twizy is scheduled to be commercially available early next year; GM’s EN-V concept will likely surface in some (possibly not two wheeled form) before long). So this is good because it means there are going to be massed produced highly efficient low cost (I saw a bottom up EN-V costing with sale price below US$5k) low emission commuter EV’s.

    To your question of ‘plans to create a device to plug…’, no, I don’t, but I suspect that it wouldn’t be very hard to hack a Twizy and you’ll immediately be at a price point FAR below where any of the special purpose PRT companies are. The problem will be getting an Auto OEM to validate your hack (or plug-in device) for, as I discovered in my last job, they are not great fans of giving away anything that might come even remotely near their potential value added… and that was when approached by a big engineering multinational. But if you build just the route planning and on-demand layer then I think there’s a good chance of one of them (on-star for e.g.) acquiring it if it’s good… but you’ll also need the auto-driving system (from google or whatever). If you plan to build such a system then I’d be interested (but that’s not my reason for this comment).

    So much for urban commuting… however I’m not sure it’s a good idea to drop the Swift MagLev concept so quickly. Medium distance travel is also a market segment that’s going to have some changes over the next years, and considering the limitations of EV’s w.r.t range it’s going to be sometime before people are using roads long distance with ultra-low emissions. You, on the other hand, seem to have a concept that could be vastly superior to existing mid-long distance travel solutions. Can go point-to-point from the middle of cities, can be fast (I assume you could get up to similar speeds to existing maglev if you used a slightly longer pod), can be easily powered by electricity, is highly efficient, and won’t crash. Sure, you need a high point-to-point demand for the economics to work, but that’s exactly what middle-distance transit would deliver (with decentralized road based systems at either end to take care of the short commutes).

    You can see in the US at the moment what a drama it is to put in a full size heavy high speed rail system. Something like what you propose here for short haul transit could be a real game changer for long haul… and would at the same time address all of the issues you encounter with the short haul system that limit viability (max corner radius and hence speed, packing density for accel/decelleration, minimum demand within x-km of station etc). I don’t know of any existing system that can provide cost effective, zero emissions, highly efficient, highly flexible schedule, high speed point-to-point transport. And for damn sure we need one – the bulk of total future distance-km travel may well be within megacities, but there’s plenty that’s outside that as well. Swift seems a great fit (at least out to ~500km – ~1000km; even if you’re only able to hit 300kph it your total trip time will still be close to a commuter jet/turbo prop once time-spent-faffing-around-at-the-airport is factored in)

    I guess you can get my email address from this comment if you’d like to discuss further? There’s a bit about me on the website attached.



    • apatzer
      December 5, 2011

      Nick, great comment. I agree that Swift would work well for mid-long range systems that are mostly point-to-point. It’s certainly cheaper than the $60B proposed for a San Francisco to Los Angeles rail system that’s expected to take 30 years to build out. If you work out the math on that system, it’s $150m / mile (or $93m / km). That’s 10x more expensive. Plus it had a huge right-of-way issue as it’s land-based, versus an elevated guideway (which also has essentially no environmental impact is its footprint is a telephone pole sized column every 60ft). So yes, Swift is a viable business in certain markets.

      While it may be viable in the mid-range market, such projects, while larger, are much less frequent than my original vision for a ubiquitous good-enough-to-replace-cars system. This means Swift would have to become primarily a “railroad” construction company versus a consumer company. It’s like being a Maersk who manufactures rail-cars versus being Toyota. That kind of business is really not my interest – point to point maglev doesn’t take advantage of all the traffic routing that could be done with PRT, or innovative station design, etc. It really reduces the Swift innovation down to the decision to do ultra lightweight aerodynamic vehicles on an elevated guideway. Which is fine, but not fun from an invention standpoint.

      • Nick
        December 6, 2011

        Hi Aaron,
        Not fun?? You get to disrupt the commuter rail, air passenger travel, and road highway networks all in one go! :-)

        I see your point though – the route/track planning software which seems like it was going to be a large part of your differentiation with the Swift concept would no longer be needed for a pure point-to-point service. In other respects I’m not sure if mid-range is so different though – you’d still need to lay quite a lot of track in either scenario, and presumably also operate this track and the vehicles and the trip planning etc etc.

        Yes, the project profile would be quite different and you might find yourself having to wait for and then bid competitively on huge projects where having no references and not being a 20Bil company worked against you.
        On the other hand, I don’t think a Swift concept would work as pure point-to-point; the vast bulk of your total system cost seems to be tied up in the track, which means that finding profitability with a long distance system will mean running this track as close to theoretical capacity as possible (a capacity which is really quite staggering to me – I did a very rough calc and it seems that a single swift track would have annual carrying capacity equal to around four times SF International Airport (39Mil passengers/annum) assuming operation 360 days per year, 18 hours per day, and running cars at 100m/sec with 1sec separation… in fact all that matters is the separation time).
        You could therefore create a really elegant hybrid system with a number of distributed feeder networks within a city (lets compare to the proposed california high speed rail system and say 50 stations across San Fran, 50 across LA, and lots of little branch lines in between) all using the same long distance trunk line. Because the utilization of the trunk line would be so high you’d be able to subsidize the less profitable and utilized feeder lines up to viability I expect… and hence the whole thing would fly. The biggest problem here would be capacity planning with multiple different stations and feeder lines all needing capacity on the trunk line and to have reliability preserved will running as close as possible to threshold capacity.
        I could see a lot of re-use of the route planning stuff you’ve already developed (especially once you want to start inserting additional pods into the trunk halfway along, and dropping them off into feeder networks part way… another aspect in which you would totally destroy the current high speed rail proposal). I realize all this is probably pretty obvious to you having just spent three months on the idea – just ‘explaining’ to understand it myself really :-)

        Another really cool thing is that the bulk of your costs are in putting up the pylons themselves. Once that’s done you could conceivably replace the motors and pods at relatively low cost, and as these are the only things defining the speed constraints of your system (the pylons and beams will probably be fine at twice the speed – at least on straight sections) your system is future proof (or resistant anyway).

        Ultimately whether this idea would work comes down to the economics of the Swift maglev concept. Present gen maglev is just too expensive, despite the benefits, and gives no distributed feeding capability. If swift is an alternative then it I’m sure there will be more than enough challenges in implementation to keep it interesting. One option could be just to build track and supply carriages for others to operate, but you could also become a consumer facing travel products company who just happens to build its own back-end. I would think if you can prove the economics and performance of this system it would be pretty easy to displace a LOT of air travel at least within the growing US mega-regions (if not between). Once you had a demo system I think finding investors for a fast/cheap/clean/scalable/personal mid-range transport system using private funding would not be so hard, especially when you see the growth projections for short-haul air travel under the biz-as-usual model.

        Nevertheless – if you’ve got the burning urge to do urban transit and nothing else then I’d still be interested in talking. The broad consensus in industry is that driverless cars will emerge gradually through ‘driver augmentation’ technologies (as is already happening) but that true ‘driverless’ cars will not be allowed anywhere on publics roads in the US for at least a decade. Sure, I scorn industry consensus like any good disruptive innovator, but this is an industry with huge inertia, huge lobbies, and a hugely paranoid (don’t let the machine drive me off the bridge!) user base. Appeals to logic don’t seem to work – people would much rather be killed one trip in a million by their own hand (they’re in control – or not, as the case may be) than one in ten million at the virtual hands of a machine.

        I had some ideas for how to get around this problem though with a distributed personal road transport system in the short term – also dramatically reduces the technical obstacles. I don’t plan to make you sign an NDA, but neither do I feel like airing them in public just yet either (maybe they are worth/able-to-be patented after all), send me a mail if you’re interested.


        p.s. Technical query – you mention hinges between the carriage and the magnet – would it not be easier to bank the rail and run the carriages at the optimum speed for the corner with no hinge? Otherwise you’ll get significant lateral loading on the linear motor – I guess this is ok up to the same g force as your max acceleration, but still seems non-ideal… or am I missing something?

  17. Robert DeDomenico
    December 5, 2011

    Hi Aaron,

    Since an epiphany moment nearly two years ago, I have been working diligently on a unique transportation concept that I think you would find very interesting. My work has included diligent research and testing, and my prototype will be ready for testing this month. My current plan is to finalize development and file patent and trademark protection in the first quarter. Until then I cannot divulge great detail in any public forum.

    I am now 45. I earned my BSCS from Rowan in 2006, and am a Business Analyst / Database Administrator / Software Developer at an Electric Generating Station, with extensive hands on experience in operations and maintenace, including six years service in the US Navy as a Submariner.

    I read your appraisal on Swift, and noted that you are still interested in pursuing a viable transportation solution. I look forward to hearing from you.

    Best regards,

    Robert DeDomenico
    Pittsgrove, NJ

  18. Devin Martin
    December 5, 2011

    I love that intelligent, creative people continue to work out the problems of transportation. I must point out, however, that at the population densities necessary to make this sytem work, there’s already a much faster, cheaper transportation solution than the automobile. It’s a bicycle. At the densities that exist in places like SF and NY, you’re simply not going to beat a bicycle for speed.

    Now, in more normal American population densities…with sprawling suburbans and whatnot…I’ve long thought a system like this with nodes spread a 2-3 miles apart would be ideal, if it’s accessed by bike. Cutting the time to “walk” to the station by 2/3 with the use of a bike changes the time trade-off pretty significantly. But Americans seem more interested in paying for gastric bypass surgery than bicycles, so such dreams will always remain mere dreams…at least in this country.

  19. kewal
    December 5, 2011

    what do you think about its possibilities of being successful in a country like india?

  20. Michael D. Setty
    December 5, 2011

    For once I’m happy to see a technogeek analysis about transportation solutions such as “PRT” that sorta gets the economics right, e.g., the “Ultra” PRT at Heathrow may have shown that low capacity PRT is technically feasible, but the economics simply do not pencil out. Your conclusions regarding PRT economics is completely consistent with my analysis for a PRT system in Winona, MN two years ago (, which also was consistent with the takedown of PRT by Dr. Vukan Vuchic many years ago.

    As with much analysis by those not completely familiar with transportation economics and technology, you do get some things incorrect when talking about bus and rail transit (and don’t think the VTA light rail system is typical of LRT; it is probably the worst performer of all new LRT systems since the 1980′s–the reasons why are another long post, but not here). In low density areas, bus and rail routes can work under some conditions, mainly that there are well-defined travel corridors and reasonably dense destinations, such as a large downtown.

    In such travel corridors, “frequent” transit service (see for a sample of a new book about this topic), can be quite cost-effective, with modes such as flexible route buses, subsidized cabs or bicycles covering the lowest density areas where fixed route transit is NOT economically viable. In the busiest corridors, rail can also make economic sense, the economics almost completely dependent on potential patronage volume. In Silicon Valley, rail does make sense in the existing Caltrain corridor and even San Jose-Fremont–though BART is greatly overpriced compared to the cost of upgrading existing trackage…another post, too long for here.

    To “get real” about transportation, e.g., to understand that improving transportation is helped somewhat by technology, but the problem is mostly economic, social and cultural, I suggest you take a look at both my white papers linked at

    • apatzer
      December 5, 2011

      Michael, thank you for the links and analysis. I’m glad my PRT numbers, not having really been a specialist in the area until a few months ago, are consistent with the types of analysis professionals perform. I’ll be reading your white papers starting this afternoon.

      • Michael D. Setty
        December 5, 2011

        As for self-driving cars (SDCs) , one commenter who doesn’t like the idea pointed out that, under current U.S. ways of doing things, potential builders are likely to use “WalMart” level sensors and other electronics, rather than very costly, “mission critical” “military grade” (sic) very low failure rate equipment. He also pointed out that the vast range of conditions encountered in driving right now may require a much higher level of demonstrated AI than has been demonstrated so far by current SDC experiments.

        The problem reminds me of the time I replaced the fuel pump/sending unit in my vehicle; the fuel pump continues to work fine but the sending unit is increasingly erratic, even after less than 2,000 hours after being replaced. There was also the LCD monitor that failed after less than 5,000 hours…then there’s the cost issue compared to standard automobiles; electric cars have a major cost disadvantage due to battery technology. What level of hardware and software reliability would be required, given the complexities of a complete AI and sensor system in a SDC?

        More specifically, how long will it require to develop the required level of reliability at a reasonable price point, say $10,000 or less per vehicle? Or are we really looking at $100k-$200k, very reliable automated taxis that could replace 25 or even 50 standard automobiles, collecting their costs through fares? Is ride sharing feasible, perhaps for small automated buses instead? As a “transit geek” I’m curious about such possibilities.

        • Nick
          December 6, 2011

          Hi Michael,

          For my money the component reliability barrier won’t be that hard to address at reasonable price once volume gets high enough. Most of the critical electronics aren’t much more fundamentally complex than the various radar/kinect/ultrasonic/gps/INS/wheel-encoder solutions you see around now and which are either already or are on their way to being dirt cheap… with the possible exception of the laser point cloud reconstruction systems which I know little about but which are likely to be at least partially replaced by optical systems (the vehicle kin ect equivalent for point-cloud, then linked into a info cloud based SLAM system like google have made/are making). Milspec pretty much just means expensive most of the time – failure rates for existing system critical vehicle systems (digital throttle and brake control for example) are already incredibly low and I’m sure this could be achieved within a reasonable price in high volume.

          The challenge will be getting the volume up – as I say above that’ll be done through ‘driver augmentation’ technologies as are already emerging. Self driving cars on normal roads are a while away simply due to industry and society acceptance. I don’t think the vehicle industry know how to sell them for one – all their existing advertising is about how great it is to be able to drive like Schumacher – they’re not heavy on how much time you actually spend stuck in traffic and how it might be nice to write some emails rather than navigate yourself…

      • Robert DeDomenico
        December 6, 2011

        Aaron, not all of your analysis were necessarily correct. Your upper limit on fuel economy calculation based on a factor of 7.5 reduction in weight and two factors of two and three producing a product of a factor of 6 for windage loss reduction does not yield an overall loss reduction of 45. It would yield an overall loss reduction of something between 6 and 7-1/2. Another way to see it is to think of a family budget. You spend $300 per month on electricity, and $300 a month on cable and phone bills. If you could recognize a factor of 3 savings in electricity, and a total factor of 6 savings on cable and phone, then the budget reduces to $150 total, where it had been $600. That’s a factor of 4 reduction, not 18. You don’t have to approve this for posting if you don’t want to. I am pointing this out for your benefit.
        Best regards,

  21. Justin Chase
    December 5, 2011

    What if instead of creating elevated rails you made ground level tubes and laid the rail in there? It seems like it could dramatically decrease the costs per m and also increase safety/reliability.

    • fgouget
      December 10, 2011

      Then you have to deal with either pedestrians or cows (depending on the setting) crossing the tracks. This brings back a good bit of the complexity of self-driving vehicles, and also means they must be hardened to deal with crashes (so more weight and cost).

  22. Dan Sturges
    December 6, 2011

    It’s great to learn that you have interest in creating a world-changing consumer transportation company. The ICT revolution is just getting rolling and will create a $3 trillion urban mobility opportunity (recent statement from several Fortune 50 companies). I too am interested in creating a new door-to-door transportation company that offers mobility that is more convenient than owning a car yet costs consumers (and the public) substantially less.

    I have been working in this field for quite some time. I’m from the different side of the tracks than you; I’m focused on applied mobility and have a background in transportation / car design. While rudimentary when compared to your Swift concept, I commercialized the first Neighborhood Electric Vehicle (NEV), and successfully (w/ partners) convinced the US DOT to create an all-new motor vehicle category. (Something NHTSA had never done before, nor since in their 40 year history). There were 50,000 of my NEVs rolling about the surface of Earth today.

    I’m curious what path to commercialization you would have pursued if your Swift concept HAD indeed penciled out and was an attractive opportunity to address? In my view, realizing leadership in this emerging market has more to do with overcoming transitional challenges than technology ones.

    I currently am supporting an elevated mass transit start-up, launching a mobility development media venture to address the cultural inertia in our country around automobile ownership, and supporting the investigation of launching an MIT Media Lab type of program with key California universities and corporate stakeholders.

    Here is a link to my website on my early mobility development media venture. You can download my recent XRDS article if you’d like to read more about my vision for next mobility:

    Thank you for sharing your work!

    Best, Dan

    Dan Sturges
    Founder, OuiCreate, LLC
    Boulder CO
    Twitter: @DNAsturges

  23. Alessandro
    December 6, 2011

    You know, your analysis is interesting, but every time I see people making assumptions based only on some ideal US scenario, I’d want to bite my keyboard.
    Here in my town, Genoa (Italy), average bus speed is around 12 Km/h (plus long waiting and erratic schedules), and the problem is somewhat similar in a lot of Euro towns; our Metro is a joke, almost useless: it took 30 year-ish to build a short toy metro that is not very useful, plus it cost, I believe, around 150m$ per Km.
    People in my position often need a car anyway for the first few kilometers (living on top of hills, walking to a station would add in my case some 40 minutes per day in travel time); then you have a parking issue; after that, you need to jump on 1 to 3 buses/metro/trains to get to work, depending on your destination. Except for some fortunates who work in the suburbs, most citizens commute every day to a dense town center and it is a-b-s-o-l-u-t-e-l-y impossible to use a car as a means of transport (unless you want to pay 3+ euros per hour to park, and often you have to waste even 30 minutes waiting to get that precious pay parking spot; and that’s on top of driving in heavy traffic that at times brinks on gridlock).
    This system is not only highly inefficient for commuters; it’s also heavily subsidized with taxes.
    There simply is no space to build or extend the road system at street level. Underground, it’s even worse, with high costs and possibly archeological issues. This, on top of the occasional flooding.
    A system like Skytran would be a dream for people like me; saying that it cannot work is the same as saying that there is ABSOLUTELY NO viable solution, and we must adapt to the idea that we’ll always waste a couple of hours every day standing on a crowded, stinky public transport car, while also being limited in our job opportunities to a very small radius away from home.
    Parking and being able to pack enough tracks where needed is definitely a problem with PRT, but possibly not unsurmountable.
    Top speeds limited by turns as a deal breaker? Really? Give me a 50Km/h urban PRT with 10+10min walk distance and people would die to get in. It would easily halve commute time for many, on top of giving lots of freedom.
    Besides many other benefits, it would permit people to move somewhere else in the countryside and still improve their commuting time; or I could easily take a job position in Milan, for instance, thanks to the intercity high speeds possible with a maglev PRT system; the social benefits would be enormous.
    A system like Skytran with elevated guideways and a limited footprint is also the only conceivable addition to a dense town structure which is commonplace in Europe.
    Initial costs are not a real problem. We spend A LOT more on inefficient public transport and roads. There is a project for a new highway bypass that is NOT going to improve the situation (I could ramble a lot on that) that is going to cost something like 15K$ per citizen. Our buses and trains bleed millions.
    Back-of-the-envelope cost estimates made by Skytran enthusiasts are probably off, because of the many unknowns, and optimistic; otoh, your estimates are also far from assessing a real scenario; it’s still all about projections and assumptions. There is no way future inventions should be ruled out on principle, based on how we estimate they will probably cost.

    • Dojomouse
      December 6, 2011

      Alessandro – I don’t think it’s so much that it’s impossible for skytran/swift concepts to beat existing road transport in crowded cities. Rather it’s that it will be very difficult for them to beat next generation shared distributed personal transit that uses roads.

      But you’re right, using separate infrastructure does make it a hell of a lot easier to leapfrog the existing disaster. Otherwise you’d basically have to ban present gen vehicles in the areas you wanted to improve for all except freight. Fair point – not everyone can modernise… and whether they’re cheap or not cars are AWFUL. Light rail may cost a lot but it works REALLY well in moderate density cities and I LOVE having cars confined to a few arterial corridors and the streets (for the most part) safe for people and bikes.

      • Alessandro
        December 9, 2011

        Automatic cars are just giving road transportation a nice boost, that’s all. When only a few rich people can use their car to access a town center and its surroundings, and they are facing heavy traffic anyway, making cars slightly more efficient is barely an improvement.
        As for the so much hyped light rail, it’s heartbraking to see so many people, often urbanites with a flair for eco-green projects and central planning, invading all the debatesphere, education and media with the righteous idea that people sholud learn to use public transportation more, because supposedly it’s more efficient (which often is not the case) and they insist on investing our future in mega-projects, creating “arteries” and concentrating traffic. I’ve heard even some advocates insist that forcing people to ride a bus or metro alongside a bunch of strangers is a worthy cause in itself, because it teaches you to “integrate” with others…
        This is madness. For most people, in my experience, a very fast, “convenient”, frequent and high capacity central artery (metro, tram, light rail, often rail…) means to ride some 3 different means of transport per travel; this in turn means 1h+ for a 10-15Km trip, often running to catch a car, then waiting tediously; various transfers walking which is extra inconvenient when bad weather is involved; getting to work already stressed from having to depend on timetables, delays, loud people complaining and arguing, being stuck standing in overcrowded smelly spaces…
        All of this being heavily subsidized by taxpayers.
        As for leaving roads for pedestrians and bikes… that is happening all too often, rendering many city centers effectively painful to reach. Bikes are a good choice for _some not all_ people in many towns. But! They are absolutely NOT A VIABLE means in towns like mine.

        • Nick
          December 9, 2011

          Which city centers do you feel are painful to reach as a result of being closed to cars? In every one where I’ve seen the transition the centre has become not only nicer but also easier to reach (I guess there would be the rare exception where the central city was NOT clogged with traffic…)

          Why are bikes not viable in Genoa? There are usually three barriers to ‘attractive’ biking conditions:
          1. Weather
          2. Traffic
          3. Hills

          Weather can be addressed to a certain extent by appropriate clothing, but sometimes this is a pain. However the Genoa weather is hardly bad.

          Traffic is a hard one (especially in Genoa I guess – I’ve never been there with a car but if Milan/Rome/Florence are anything to go by I don’t want to!). But it’s resolvable if you have a planning policy that supports bikes.

          Hills used to be hard, but with electric bikes they’re easy.

          Anyway. Let’s consider just skytran vs automatic cars for urban use. What is the big difference in your opinion except for the fact that the skytran system is physically separated (which does make things much easier I agree). Both solutions would allow publicly available vehicle fleets, both would be much faster and less congested than existing solutions, and both would be cheaper than existing solutions (through higher capacity factors).

          Is your point that the road system in Genoa is already at capacity and that the only way to increase capacity is to go for elevated tracks? Because if so then I’d argue that the other way to increase capacity is to have far better driver behavior, massively improving throughput on existing infrastructure. This is what driverless cars could deliver.


          • Eph
            December 9, 2011

            Nick, I enjoyed reading your contributions here, but please elaborate on how using driverless cars would end up “massively improving throughput on existing infrastructure”.

            If anything, people take unwarranted risk by not allow sufficient stopping distance between vehicles, running lights etc… People also use facial cues/gestures/sounds to resolve conflicts making traffic flow more smoothly.

            Until ALL vehicles are automated, there won’t be much improvement and may actually be a reduction in capacity. Promises of shorter following distances and closer spacing ignores some rules of physics that would make driverless cars safer as they MUST be in the early days. That following distance allows a vehicle to brake BEFORE hitting the vehicle in front that just go clocked by a cement truck. That space between vehicles allows room to avoid an obstacle (like a cyclist knocked off her bike and into traffic by a carelessly opened car door) should things go south.

            PRT actually allows all of the good things expected/promised/hyped about driverless cars to actually be realized today. ALL vehicle interactions are automated, no external forces (like cyclists and pedestrians) come into play. All vehicles are at the same technological level. And all vehicle are non polluting and as non GHG producing as the electricity grid (or powered by clean energy since the energy cost is reduced compared to fossil fuels).

            A dualmode(DM)/hybrid PRT would allow people to drive themselves in low population density areas, then use a PRT guideway in high population density areas and busy roads/highways. We shouldn’t be wasting money on large LRT projects – in Ottawa, such a project will cost $5 Billion (likely more) and if it serves 15% of the ~1 million population (not likely) will cost ~$33,000 per rider and ~$5,000 per person. It will also have to be subsidized typically dollar for farebox dollar. I think we can do better.


          • Alessandro
            December 14, 2011

            Hills. This year I’ve seen one woman trying to use an electric bike regularly to get home in my street. It lasted 1 week.
            Besides, when most streets are one lane per direction, there is very little room for the adventurous biker…
            Planning policies that support bikes are pet projects with really no use, with a small loop in the only part of town where you can afford to waste some space; it infuriates me, because people feel warm and fuzzy by self congratulating for their blindly adhering to a trend… because showing you comply with the eco mantras is the only thing that counts; the fact that your actions make no sense is irrelevant.
            As for automated cars, I already acknowledged that they improve road capacity, but only to a point. We’ll get them, and the related benefits, anyway. Adding a separate, elevated system, designed to be faster, means improving transportation in a far more profound fashion. It’s an addition, not an alternative.
            When your car is driverless critical roads become less prone to congestion for a given amount of cars per hour, but the added convenience generates way more traffic, more than counterbalancing the added efficiency.

          • Nick
            December 15, 2011

            Hills seem to be the weakest anti-bike argument to me. Historically, yes. Today, maybe yes if you have a rubbish electric bike. Tomorrow? Come on. Lance Armstrong gets up hills pretty well on a bike, and a halfway decent electric bike has around 40 lance-armstrong-kilometers inside it. I mean if you want to be picky about it we can just say ‘electric scooter’ with nominal power output easily in the several kW range. Sanity is the main speed limitation, not potential electric drivetrain power.
            Weather and safety I can accept as realistic future barriers, but not hills.

            Which leads me to your next comment – “Planning policies that support bikes are pet projects with no use”. Huh? Did a bike pick on you when you were a child? ;-)

            Take Amsterdam – a modern bustling city with great bike infrastructure and huge adoption. The weather there is pretty bad. The traffic safety issues are rendered minimal by the intelligent layout of pathways. The main thing that’s different from everywhere else is that Amsterdam is FLAT… and this flatness is rendered irrelevant by the new generation of electric bikes. I’ll happily agree that poorly integrated bike infrastructure done badly is a eco-bandaid that’s meaningless… but that’s no reason to condemn bike infrastructure done WELL.

            As to your final point on increasing efficiency driving increasing user adoption – true. But the same thing will happen with any elevated system.

            I can definitely see the benefits of an elevated railway, but it’s certainly not the only option, nor necessarily the best for all applications.

          • Alessandro
            December 20, 2011

            As for electric bikes: there is a clear difference between what is practical and eventually widely adopted, and what you *could* potentially do, if you were _really_ motivated, usually for green ideology reasons.
            My town has a really high percentage of scooters and motobikes, due to the sheer inconvenience of cars when traffic is intense, plus the parking problem.
            And yet, I’d say electric bikes are nowhere to be seen. If they were a viable option, at least _someone_ would be buying them. When shopping for a bushcutter, I was surprised by the abysmal performance and high price of electric models. Ten years ago they were 10 yrs away from being a viable option. They are still 10 yrs away.
            The woman I saw using a bike for not more than a week was using an electric bike, the only one I ever saw. She was pedaling madly anyway, because that slope in various places is too steep for a weak electric motor.
            “If you really want it, you can use an electric bike” doesn’t cut it.
            Besides, scooters and motobikes are polluting more than cars; people use cars anyway, so to get a 2-wheel vehicle you have to pay insurance and other costs for an extra vehicle, while clogging streets during winter bad weather, when people shift en masse to their car. On top of that, people I know that use scooters extensively get into some serious accidents from time to time.
            When roads are narrow and overburdened by traffic, you can hardly feel at ease slaloming around cars protected only by a helmet.
            Advances in electric motors and batteries will _eventually_ give us viable scooter alternatives, but this will only solve the concentrated pollution problem.
            As for your example of Amsterdam, I believe it represents perfectly the narrowmindedness of most eco-friendly proposals. I was explicitly describing the infuriating attitude of city officials in my town, who think posing as friends of the environment is more important than doing things that make sense, so they committed themselves to a pet project of a bike lane that is a useless small ring in the only part of town where it is possible to create one, hinting that they want, too, to gradually increase the road portion reserved to bikes, because they want to blindly join the ecoTaliban bandwagon. No fact check whatsoever, because bike lanes are the fashionable choice for politicians.
            And what do you reply to that? You bring up Amsterdam!
            How can this possibly change the meaning of what I wrote?!?
            Let them ride bikes every day. Let them have bike lanes everywhere in Amsterdam. It works there. Not all towns are equal!
            What is natural in some place, is impractical somewhere else. I’ve been in Cremona, you see lots of old wives getting around with their old bikes. (I supposed they are hipsters, because they used bikes in cities before it became popular…)
            You can facilitate that with bike lanes, but it was already a way of life before any green movement. Elsewhere, where it’s not practical, you cannot fake it by building pet projects that remain mostly unused while creating inconveniences.
            You made a straw man out of me, by saying that I shouldn’t “condemn bike infrastructure done WELL”… who said that? I was talking of my town. The fact that something works somehere is no reason to act as if it should become the norm everywhere!
            Remember the whole point of this entire webpage (and other anti-PRT websites as well): 1.we feel fine using and possibly improving our car and bike road infrastructure, so there is no need to develop PRT systems. 2.Since on paper they seem not to be viable, no one should really design and test them.
            But this means renouncing to do research due to preliminary considerations (which is absurd); on top of that, (the following is not shouting, is higlighting) IGNORING POTENTIAL BENEFITS OF A NEW SYSTEM BECAUSE WE FOCUS ON OUR LIMITED EXPERIENCE, IGNORING THAT LOTS OF PLACES AROUND THE WORLD HAVE DIFFERENT ISSUES AND WOULD LOVE TO USE WHAT WE DEEM USELESS.

          • Nick
            December 29, 2011

            Hi Eph,

            There’s two bits to your comment – firstly the potential benefits of PRT/hybrid-PRT which I don’t want to argue against (as I think I might have inadvertently with Alessandro) as I totally agree – I think PRT done right and in the right mix with existing infrastructure can be a very good system… which is why I’m so interested in the cost profile that Aaron has calculated and the potential for improvement. So basically no argument there – especially on the hybrid system which I think could bring the best of both worlds in most cases. Though the reason I think a hybrid PRT system is the most interesting for long distance is not that it allows separation of powered vehicles and cyclists… but rather that it allows the separation of heavy vehicles (cars, trucks, SUV’s) and light, highly streamlined vehicles (such as Aarons PRT concept). It’s hard to get acceptance of ultralight vehicles under mixed used conditions, especially in highway environments, as people are worried about getting crushed. Not saying I think PRT always works, just that philosophically I can see a place for it once volume gets up high enough to justify the cost of a dedicated single-use ‘corridor’ (much like other mass transit… just hopefully with lower cost!).

            Ok, onto driverless cars where the first part of your comment focussed – I agree, in the early days you only get a limited number of the benefits as many cars are still constrained by a person behind the wheel. In some environments you can address this (for example, highways could have a dedicated lane for self driven vehicles… or in fact any vehicle with the ability to form up into a train on highways which is vastly easier to do) but in others the early benefits will be more on safety than on capacity. So it could be that the transition takes quite a while – maybe 20 years from first introduction for the majority of the benefits to be realized (10 years for it to filter from luxury vehicles to economy – like airbags – and another 10 years for the majority of the economy vehicles to be replaced with the new tech).

            Once this is done though, and we can work on the assumption that all vehicles are robot-driven:

            On why robot driven allows reduced following distance: The 2 seconds (more usually 1) that most people leave between cars doesn’t really help you if the car in front gets clocked by a cement truck or a cyclist gets knocked into your path. You either swerve or hit. The spacing helps when you’re both braking under relatively similar conditions (and hence deceleration). Basically you need around half a second (if you’re paying attention) from the brake lights of the car in front going on to process the event, shift your foot to the brake, and hit the brake. The other half second of space is used up by the integral of the difference in velocity you now have… and all too often is not enough! Most of the time people are saved by the fact that the car in front is typically just ‘slowing down’, not ‘slamming on the anchors for dear life’, which means that despite the delay in reaction you can make it up by decelerating harder in the early moments. The cases where the car in front DOES really slam on the brakes are usually the cases when they get rear ended – differential velocity becomes too high in the reaction time and can’t be corrected without a crunch. Now, robot cars get around this firstly because their reaction time is more likely a few 10′s of milliseconds (or less – I’m just assuming some fairly slow filters on the sensing channels to avoid nuisance responses). Secondly, because most such systems assume increasingly advanced vehicle-to-vehicle comms, and the routes are planned in advance, and most of the ‘slow down’ events are known in advance… the following vehicle actually knows to slow down before the car in front even starts decelerating. This allows you to dramatically reduce the following distance without changing the chance of a rear end by much. Let’s not say zero… but perhaps half a second, which is around 7m at 50kph – you still need some buffer to account for merging traffic etc.

            Facial cues, gestures, unwarranted risks: True – but I’d argue that most of these are the result of the poor systems we have in place today… people make the best (and overall do a good job) of a usually bad/ambiguous situation. I mean if you get to the point that you’re trying to improve traffic flow and prevent collisions by relying on people to interpret frustrated gestures at 10m through a window in the rain then your system is obviously not going to have great bandwidth :-) These gestures and risks are usually both symptom and cause of the situations where traffic throughput collapses.

            This brings me to the most interesting thing about how robot-driven vehicles can improve traffic throughput: by NOT COLLAPSING it. I was looking into this stuff a lot a couple of years ago, and found some great studies (and a cool video on youtube) of the capacity of various transport solutions under different conditions – I can’t find the links right now but I think some of it is probably lurking around on Brad Templetons blog.
            Anyway – the general understanding of how robot-driven cars improve the traffic flow is that:
            1. Lane capacity (vehicles/hour) at most velocities is largely a function of vehicle separation (say 2 seconds). If there is a vehicle every 2 seconds, then there are 1800 vehicles/hour (speed is not so relevant for capacity… though obviously makes a difference to travel time!). This is the usual figure used for lane capacity. Compared to commuter rail, with a theoretical capacity at maximum ridership of around 15,000 – 20,000/persons.hour (To be fair, cars at max ridership with 4/car could get to ~8,000).
            2. Robot driven cars can follow at much reduced distances… so if we use the same situation as above but are following at 0.5 seconds then the theoretical lane capacity goes up to 7200 vehicles/hour. Great success!

            This is certainly partly true… but not the most interesting thing. The crazy part is what happens with human driven cars vs robot driven cars at that 2 second separation point – lets keep that as our target to avoid confusion with the other safety issues.
            Robot driven cars keep on cruising along at nominal speed for the road, and you hit whatever limit you’ve decided for that lane (say 1,800). Human driven cars, on the other hand, when trying to push past this limit (inevitable as you add demand in the form of more rushed commuters) actually collapse the free flow of traffic even if there is NO additional disruption. Basically the problem comes from peoples reactions and the associated feedback loops – if you are barreling down a freeway and are slightly too close to the car in front and you even THINK they might have touched their brakes… you touch yours. And the guy behind reacts, and so on, and you get a big ripply in traffic. Having a short distance between the cars means this ripple is amplified (people hit their brakes harder) and usually repeats (people come off the brakes onto the accelerator… and then shortly decide to brake again) and everything goes downhill and eventually you end up with lanes of traffic on an ‘unobstructed’ freeway (or any other road) where some of the vehicles are motionless! This is a classic traffic jam, and the numbers I saw for lane capacity once this happened were around 400 -> 500 vehicles/hour. Here’s an explanation – you can also search ‘shockwave traffic jam’ for the driving in a circle video which is a compelling real world test. (

            Here, robot-driven cars avoid the problem by not perpetuating it – they DO have system-level visibility of what’s going on and can adjust speed and following distance accordingly. Even if flow doesn’t “increase” as such, by ensuring it doesn’t collapse you can increase the effective capacity of a lane by a factor of 4.


            At things like roundabouts, traffic lights, merging situations etc the capacity increase is basically the result of increased packing density and better merging. There are lots of sci-fi looking videos of cars streaming through intersections in both directions simultaneously and just missing each other. No theoretical barrier to this but I’d expect it be a while away! Even if you didn’t have such sharing though, imagine what could be achieved by taking human reactions and risk attitudes out of the way. You no longer need an orange light, nor that wait period after the change to red, nor the period while people realize the light is green and begin to move. Rather the traffic flow in one direction would follow hard on the heels of traffic flowing the other with no wait period, simply because of faster response loops and better system observability.

            Finally, and most gloriously for me, you would never have the situation where some clown enters an intersection despite there being no room on the other side to leave, which is an absolute killer in urban driving!

  24. Seth
    December 7, 2011

    Wow, to find a decent analysis on transportation on the internet is quite cool. Electric tether idea is also cool for city to city transport. Swift to the airport would be useful.

    I think your cost estimate for ropeway transport is off. Using the cost to build in extreme mountain conditions is much higher than urban or rural ropeway transport. Gondola transport is old and should be cost effective.

    If the pods could attach and detach from ropes using off the shelf gondola equipment. And cheaper ropeways could reach 30-40 mph with such pods. Couldn’t the maglev system be scaled to something like 1 out of 5 stations, with 4 surrounding stations being ropeway systems? Users wouldn’t have to change pods, it would just add some time if they didn’t live by the express/hub locations.

    It would also solve the parking issue since you could hang all the pods out to dry. It also focuses population over time around the main stations while offering a lesser degree of service for those that choose to live in less dense locations.

  25. Ken
    December 7, 2011

    Excellent analysis, especially on the curves, but as some others have pointed out, there are some flaws in your thinking. The biggest is that while it might be less expensive on a theoretical mile to build a new road, in more mature markets, adding a new road is essentially impossible. This is why L.A. keeps expanding it’s subway system at a staggering cost. Because there is no where else to build roads.

    I often dream of PRT while I sit stuck in traffic on Wilshire Blvd. heading East at 5PM from Santa Monica. It can take an hour to go 10 miles. If you’re lucky.

    Rather than focus your analysis on Palo Alto, a small suburb with little traffic, try doing it for LA. I’m guessing that (1) two lane PRT will work and (2) it will cost far, far less and serve more people than the proposed subways or expanding highways.

    Just because the math doesn’t work in one situation doesn’t mean it wouldn’t work in another. Multi-lane PRT? Where do I sign!

    • Alessandro
      December 9, 2011


  26. Dojomouse
    December 8, 2011

    Hi Aaron,

    I was feeling uneasy about some of the costs you estimated for the track per km – not for the maglev systems which I completely agree will be very expensive, but for the track itself.

    Detailed calculations below, but basically I get only $41,000/km for the complete guideway steel cost. Even doubling the cost to get to finished steel, this is still only $80k/km. So the problem with elevated PRT certainly isn’t steel vs asphalt price!

    Further, I think your economic estimates would also change if you costed the right of way. An urban road could easily run $4M/km before anything is even built. Astronomically more if, as Alessandro mentions above, you need to knock down existing buildings. Details below.


    When I checked the numbers using steel beams, 40kN max loads per beam section, 30m separation between support columns, and the 4m truss/7m pole you show for the supports I ended up with the following figures using HE-A steel beams:

    Guideway: Use 100A steel section – deflection at max force is 0.32mm, cost 15$/m @ steel $900/ton. Two required for two directions.

    Cross piece: Use 120A steel section – cost $18/m

    Support: Use 160A steel section – cost $27/m

    Guideway Steel cost function: $/km = 1000 * Guide$/m * 2 + (1000/30) * [(4 * cross$/m) + 10 * support$/m)]

    -> $/km = $30,000 + $2,400 + $9,000 = $41,400/km

    Road right-of-way = ~8m * 1000m/km = 8000m2. At $500/m2 (cheap for urban land) this ROW costs $4M/km.

    • Dojomouse
      December 8, 2011

      Ok so the $500/m2 for urban land is probably too high – perhaps more like $100 given no need for power/drainage/road. Still a significant sum. And would be higher in premium suburbs.

    • Isaac
      December 13, 2011

      Hi Dojomouse,

      I worked with Aaron on his cost estimation of the rail and support framing, and I’d like to briefly respond to your comments.

      $900/ton is a low end estimate for structural steel cost of material and installation. A more common price would be in the neighborhood of $2000/ton. The framing members required for the swift system would need to be substantially heavier than those you’ve chosen for your computation. This is not only a matter of calculating simple vertical deflections. I built a fairly robust model of the swift system in RISA 3D, a finite element structural engineering software, and the member sizes were approximately 4x to 5x larger than those you’ve chosen for your estimates. The rail size in particular will be quite a bit heavier if the system were to use entirelly 30m spans, perhaps 10x or more times the weight you’ve chosen at this span. Cost estimates should also include the price of foundations.

      If you’d like, I can go into more detail on any of the above, please let me know.

      Thank you,


      • Nick
        December 29, 2011

        Hi Isaac,

        Thanks very much for the reply! I bow to your experience here – I’m not a civil engineer – but will try to explain my assumptions in the search for an answer.

        Firstly – happily agree that $900/Ton would be cheap steel! This is why I doubled it to get to the final figure of $80k/km (at $1800/ton for steel sections). Happy to call it $2k/ton for future calculations.

        Likewise, I didn’t go to anything like the extent of FEA model – rather just a few simple hand calculations and a material data sheet for steel sections. But I’m surprised the results really indicate that this much strength is required. Again, I can’t really comment with any authority, but did you benchmark it somehow against other monorail systems? Or elevated walkways? What’s the main driver for strength requirement – speed in corners or… ?

        Yes, have to consider foundations…. but from a material perspective this is concrete and holes (and rebar) and hence will not be more expensive than roading.

        I just took a look at this: which seems to show extremely high costs also (on the order of $40mil/km best cast for full systems (KL, Malaysia)) for monorails. These are for vehicles that mass several tens of tons though.

        I guess it’s just non-intuitive to me that you need so much steel to support such a small mass as a swift-equivalent module. What I haven’t included is the mass of the linear motors, which perhaps you have, but that’s because I’d prefer to first understand how much cost maglev really adds… and whether it’s MAGLEV-PRT that’s unrealistic for urban transit, or PRT in general.

        Do you have any comparable systems you could point to? What safety factors did you design with?

        Thanks for your time,


        • Isaac
          March 15, 2012

          Hi Nick,

          Sorry for the delay in responding to your message. I don’t have time to go into great length for all your questions but the biggest driver in steel member sizes is actually not strength, but serviceability (deflections). If you run your calculations again for a simple span, make sure you account for the self weight of the rails themselves. The reality is that without experience in these matters it is common to visualize steel beams as perfectly rigid sections that do not deform, but this is simple not true, especially at this scale. Trying to use such shallows members would result in deflections that greatly exceed the tolerances of the Mag Lev system. In the case, the primary load on the rails, which span 30+m, is not the individual rail cars, it is the self weight of the rails themselves. In structural engineering terms, we’d call this the system dead load, while the cars and associated equipment would be called the live load.

          I hope this gives you some direction on where to look for additional information.


  27. Andrew F
    December 9, 2011

    Your conclusion that PRT is uneconomical hinges on your assumption that the maximum economical investment is $1000 per person served. By this measure cars, including self-driving cars, are also uneconomical as they require investment in the range of tens of thousands of dollars per person served. Your conclusion is highly sensitive to this assumption of investment per capita. You might want to do some sensitivity analysis on it.

    • Nick
      January 4, 2012

      For a benchmark: in Switzerland there is a ‘GA’ public transport subscription that allows free use of all public transport (trains, trams, buses, ferries) comprising a comprehensive national network. It’s very good, but not better than a Swift system would be… and it costs ~$3,000/year.pp. A lot of people have one, and no surprise when you consider the annual TCO of a car. With a system such as Swift where a huge fraction of the total cost is tied up in the track/motors, with a life around 20years+, I think capex target of $1000.pp is very low. Nice if you could get there, sure, but by no means a write off if it’s 10x as much.

  28. PRZ
    December 10, 2011

    as others pointed out, your hypothesis is based upon low density area and there are many places where cars are simply a very poor option for individual transport.
    Where I live (nearby Paris, France), car travels are used for less then 50% of the individuals journeys because the area is too dense, the gridlock is permanent and there is no possibility to extend the roads. Average bus speed is 12km/h (8 km/h inside Paris) and buses are aimed to be distribution branches, so are doing many detours. Average time to go to work is between 45 min and 1 h for quite short journeys (~10-15 km) .
    What is quite surprising is the speed performance you target for your system. 200 km/h ? It doesn’t make sense in an urban area as you underline yourself, cornering and insertion in the traffic needing way too long acceleration/decceleration lanes and huge power needs. That is why a lot of PRT systems are based upon a maximum speed of approximately 40 km/h. They does not look as fancy as your proposed system, but this is sufficient to allow in many European cities huge improvement in performance over ANY other transport mean.
    A lower speed greatly simplify engineering, notably motorisation. This shall drive to much lower cost than your calculations. Lower speed mean that you could use elastomeric wheel with a very long life expectation on steel way. Paris Metro pneumatic tyres last 1 million kilometers. Even if it does requied more maintenance than a maglev way, this is not that dramatic. appropriately sized ball bearing could last quite long time. Also, with reasonnable acceleration, this low speed maintain for a light vehicle your peak power somewhere around 10 kw, which could be done with very low weight permanent magnet motors (< 5 kg). Very simple motor-wheels couls be used . Low power also means easy electrical distribution with a power rail. If the reliability or maintenance of a power rail became a concern, you are within the power range of non contact power transmission used in industry carts (with somewhat higher cost and not negligible loss of efficiency). An advantage is that non contact power transmission can also provide your telecom.
    And for junction between dense areas, the same motor could allow higher speed (70-80 km/h), provided that, effectively, you build long acceleration lane. It is not a problem if your steel way is low cost.
    In short, you give yourself target too difficult to attain and at the end tell you could not reach them ?
    I think we shall focus on present needs, not on bright sci-fi perspectives, even if they looks way fun. And the future needs are not higher speed, but lower overall energy consumption. The competing system shall not be cars, but electric bikes…

  29. Richard Rabinowitz
    December 12, 2011

    If you can platoon a bunch of self driving cars, you might as well attempt the next step: connecting them to one another and to a “mothership”. Since roads are ubiquitous anyhow, we might try the following experiment: designate some wider-lane roads as corridors along which “motherships” can run. It should be a simple matter to design one which several podcars can hook up to, from which passengers can get up and eat a meal. Think of it as a roving rest stop, which it essentially is, or perhaps as a railroad dining car. (And I suspect that, with robot technology, one can make a “mothership” out of a railroad dining car: true, you’ll need to have some legal changes and maybe a lane widening or two, but if you can ship a Boeing 757 fuselage down a stretch of highway*, you can make a “mothership” from a railroad dining car.)

    *Flight 1549′s trip to the Carolinas by highway comes to mind.

    A simpler solution might be to hook podcars to each other and let people walk between podcars, making, for example, a pod-office or a pod-lounge.

    The future of transportation will merge cars and transit.

  30. Richard Rabinowitz
    December 12, 2011

    In low-density areas, asphalt will be king; in high-density areas, there will be more asphalt than rails, but there will be some rails. Freight railroads might find some competition from robot trucks. There’s a solution to this: rent out the railroads to private robocar users, and let them onto the steel rails (do it yourself railroading). Also, robotrucks might find the rails useful. It’s an elegant solution to making underused freight railroads (and they are underused in some areas) more useful.

  31. Richard Gilbert
    December 13, 2011

    Please give the basis for the following statement:
    “Given a cost of $8m per kilometer, stations must serve about 8,000 people each to be economical.”

  32. Matthias
    December 13, 2011

    I read the report and a there are a few things i do not like.

    Cost A: While such a system has never been built you make some assumptions which are not well thought. First you excludes the cost of land. Of course you can built a very low cost rail or road if the land is free. But in urban environment the free space is very scarce. So new traffic routes have to be built elevated or underground.
    Cost B: Next wrong assumptions are the materials. Maglev use Aluminum coils and not copper coils. Simple as many coils are needed and Aluminum is cheaper than copper. Transrapid also uses aluminum coils.
    Cost C: Obviously this PRT type claims to capable of running 200km/h. Within a city there is no need to build all tracks to 200km/h. As the motor is built to the track a 50km/h track would have a much lower cost as a 200km/h.
    Network layout: There are not a many on/off ramps needed just before and after every town. Within the city vehicles can travel at lower speed so the speed between vehicles are matched.
    Capacity: A very common misunderstanding is, that capacity is higher if the speed is higher however this is only the case for fluids not for any vehicle. As a tracked vehicles must comply with the so called brick wall rule. That means any vehicle must be able to make a stop before hitting the vehicle in front of it, given the first vehicle hits an imaginary wall. Spacing of vehicles traveling 200km/h will be 47s when a deceleration of 1.2m/s^2 is used. Obviously running 2 person vehicles at 200km/h gives a very low capacity and is not likely to financially viable. Maximum deceleration is limited by law even modern trains could accelerate and decelerate faster. Even high speed trains couple two sets together to increase capacity instead of running the to sets after each other.
    For the same reason highways and roads have their maximum capacity between 60 and 80 km/h. Its only logic that a PRT has a the same capacity like a road for vehicles per minute. Slightly higher as there are no human factors and silly behaviors like lane changing. So the way to increase capacity it to put more passengers into a vehicle. Instead of using a SUV with an average 1.2 person per vehicle use a Jeepney with an average 12 persons per vehicle and the capacity of a road just has increased by a factor of 10. Another way would be coupling vehicles together like the railways do and uncouple it when the use separate routes. But this will be to complex for a PRT.

  33. GiorgioXT
    December 13, 2011

    Compliments for the very well made analysis, its not usual to find such a good work.

    Some randomly notes :

    Maglev : its from the sixties Transrapid that I’m awaiting for the break-in of this technology, but I’m seeing that even in China its future is rather uncertain; anyway, an alternative avalaible is air-cushion suspension, used in some people mover and industrial systems that could offer part of Maglev advantages at a fractional cost and complexity.

    Gondola/Ropeways : You’ve taken the costs from an example in Utah mountains; is correct, but the real costs could be lower by a 40 to 60% approx, since the gross of the costs are in the two main stations … a lift double in length that of Panorama will cost just 15% more.

    Main point : your concept is neither a personal transport like a car (lacks the flexibility of space, carrying goods , exclusive use and final destination choice) nor a mass transport (lacks the capacity – you state 2000 vehicles/hour handled by stations, but at 1,9 seconds spacing , plus 1 second for transit -w/o stopping you got just 1241 vehicles/hour throughput)… so seems very difficult to find an application in urban/suburban environment … FOR PEOPLE TRANSPORT.

    Instead, try to think SWIFT for an automated urban goods distribution – here you have : fixed routes and destinations, closed-loop possible circuits, and someone tha already pays a lot for having vans stay immobile in traffic for 75% of time…

  34. Igor
    December 14, 2011

    Very interesting piece of work, Aaron.
    But like Alessandro, I just bit my keyboard because of all the US centric assumptions. I live in Amsterdam, which is part of a metropolitan region with some 10 million inhabitants which we call ‘Randstad’. Traffic between the cities of the region is hell. However, the central area of the Randstad is called the ‘Green Heart’ and authorities are struggling to keep it the open green area that it is today. More roads are definitely a no-no. On the fringes of the Randstad you will find a lot of open water wich also prevents road building. Maglev might be the perfect solution for the region. I know the option has been studied, but the costs have been prohibitive till now.

  35. Jay Andress
    December 14, 2011

    Besides the cost issue of the track going into local neighborhoods there is also the appearance of the track. Your initial basic assumption that tracks could reach local destinations was rather flawed from day one. You don’t even consider rural locations which would make your initial assumptions even more flawed.
    There is a solution to this problem…use smaller, lightweight vehicles that disconnect from the rail to reach local destinations. Eletrified rails would allow electric vehicles unlimited range and solve the battery problem for electric cars because vehicles are recharged while on the track.
    Your other basic assumption of using maglev is also flawed because the rolling resistance of small electric cars is so slow anyway, that the benefits of maglev are minimal. It definately doesn’t justify the cost and complexity.
    Keep it simple, keep it light, maximize the great benefits of electric motors and we estimate you can go 100 mph, have automated driving and fuel efficiency improvements of over 300% compared to the automobile…plus solve global warming, traffic congestion and improve safety…a nice little product for today’s world.

  36. Yan Piero
    December 21, 2011

    Hi Aaron,

    Congratulations on this idea. Every day I’m thinking of new ideas of tools that would make life easier. I really admire you and I feel we have a lot in common. I am currently starting my own PFM for Latin America which I would like to talk to you about among other new business ideas I’m sure you will love.

  37. Chris Xithalis
    December 24, 2011

    Hello Apatzer,

    my name is Chris Xithalis and I have devoted some time to PRT research like you did. I too have developed a PRT concept called Hermes ( ).

    I read your post carefully. There are many similarities between Hermes and Swift such as the minimal 2 person vehicle. I also got a bit surprised with your maglev scheme, it’s very close to what I envisioned for Hermes (I even got some neodymium magnets and toying with electronics but haven’t achieved levitation yet – too busy with my normal work).

    I do have some questions:
    1)Why do you choose such a high speed that makes things so hard for Swift?
    Hermes vehicles travel at 60-70km/hour. Simulation (which is available for download) shows that total trip time including walking is very satisfactory and a big improvement compared to mass transit or congested cars. I draw my experience from the greek capital , Athens where e.g. a 15km trip in 20-23 minutes is VERY good. Is the situation dramatically different where you live?

    At 60 km/hour, Hermes vehicles don’t need to slow down at turns. The ‘naive’ thinking that minimum distance between vehicles is very close to the average distance is the basis of the simulation resulting in capacities in the range of 10.000 vehicles/hour. If inter-city travel time is of concern you can always make a fast line , with very few interchanges , between cities.

    2)Why use 2-way lines instead of 1 way only? This helps dramatically in enlarging turning radius and simplifying intersections. It only adds 1-2 minutes of extra trip time on average as the vehicles will need sometimes to ‘go round the block’. It reduces guideway cost too. Of course the network now is comprised of loops (or a grid).

    I hope my observations are helpful.