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Personal Rapid Transit grids
Proposal for  Contest 2011: National by  fry

Personal Rapid Transit grids


Install connected Personal Rapid Transit grids over the urban and suburban areas that house the densest 50% of the US population.


Executive summary

A large set of national problems are caused by our car-based transportation system. It is directly expensive for individuals, second only to housing. It is time-consuming especially due to the slow speeds in congestion. It causes air pollution which causes respiratory disease and global warming. Car accidents cause 40K deaths and hundreds of thousands of injuries per year. The demand for foreign oil causes wars. (As I write this, the US is fighting 3 hot oil wars with, I suspect, more on the way.) We can eliminate cars, buses, subways and short-haul airplanes from our urban areas with a grid of 1-mile square cells of magnetic-levitation guideways, 20 feet above a city containing 2 person 'pods' that are waiting for customers at an average distance of just over 1/4 mile from every point in the grid. These pods use less energy and money per passenger mile than any practical electric car, bus or rail (light or not) and are safer and faster. At the top speed of 150MPH, they are faster city-center to city-center than current air travel for cities several hundred miles apart. They beat high speed rail not because their top speed is faster, but because you don't have to wait for them or travel so much to stations. At a fare of 10 cents per passenger mile, (compared to more than 50 cents for cars and even more for existing mass transit) the system can pay for its capital and operating expenses off of rider fares with NO government subsidy, unlike all mass transit in the US today.

Skytran pod prototype and city integration

Left: SkyTran prototype at NASA Ames.               Right: Artist rendition of Skytran in a city.  


Christopher Fry, Research Scientist, MIT Media Lab. I've followed the development of Personal Rapid Transit systems since 2007 and identified the best technical and economic features of all proposed systems. I've developed spreadsheet models for Boston and Detroit of costs involved for PRT'ing those cities.


The most energy efficient and economical of the numerous PRT systems that have been proposed is called SkyTran. The Skytran guideway has a cross section of about a square foot. The pods hang beneath the guideway yet are magnetically levitated by the guideway such that during normal operation, the pod does not touch the guideway. Linear electric motors comprised of the bogie that is attached to the top of a pod and the guidway itself propel the pod. The pod contains two seats, one behind the other. The guideway is suspended by utility-like poles 20 feet above the ground. Pole spacing is 30 feet, with each pole having a footprint of about a square foot.


A station is placed every mile along a guideway, but it is off the main line.The core of a station is just some extra track that runs parallel to the main track where pods can park for loading and unloading. This means that if you don't want to go to a station, you just bypass it at full speed.

A typical station can contain 5 pods. There is a staircase up 14 feet to a small platform where riders board pods. The platform and stairs will have a roof but no walls. Stations are simple and cheap, unlike rail stations. The guideways are arranged in a rectangular grid with a cell size of 1 mile x 1 mile. With stations in the middle of each one mile segment, the maximum distance to a station from any point within the grid will be 1/2 mile, with the average distance of a little more than 1/4 mile. Most people can cover 1/4 mile in several minutes of walking. Since the need for cars are drastically reduced, if not eliminated, such an area is ideal for bike sharing. We anticipate each PRT station to also be a bike-share station, with additional bike share stations in the interior of each cell.

Guideway Grids

A small city such as Boston could profitably have a 30 by 30 mile grid over it for a total of 1800 miles of guideway (2 miles of guideway per square mile). This is enough to cover more than inside Route 128. Many suburbs would be covered. Each PRT'd city would be linked by PRT to its neighboring PRT's cities. In the case of Boston, that would include at least Worcester and Providence, which in turn would connect to other cities such as Hartford and NYC. Intracity pods would travel at 30 MPH while intercity could travel at 150MPH, making Boston center to NYC center in a little over an hour. Even more impressive is suburban Boston to suburban NYC in roughly the same amount of time. NY and LA are 2500 miles apart which is 16.6 hours at 150 MPH. Though planes travel about 500 MPH, if you include getting to and from the airports, security, the time it takes to buy a ticket on perennially broken web sites plus the inconvenience for having to leave when you thought you wanted to leave a few weeks ago as opposed to when you actually want to leave NOW, 16 hours isn't far from the REAL air travel time. Plus you can have dinner with your college buddy in St. Louis at no extra charge.


Pods are driven by computer. That means you can text all you want without endangering your or anyone else's life. Or get your homework done. It also means that pods can carry freight with no passengers. Because pods are electric (quiet and pollution free) they can go inside of buildings. Stations can be installed inside of buildings, preferably on the 2nd floor. Pods can go direct to the assembly line exactly where the parts are needed or at the end of the line for shipping finished products. Retail outlets can have goods delivered INSIDE the back of the store directly into inventory. Normal pods without seats can hold a refrigerator, just about the biggest thing you can get through a house's front door. We anticipate some larger items being redesigned into pod-sized modules, to be assembled at their final destination. Larger items and volume might still be delivered via truck, perhaps limited to the hours from Midnight to 6AM. Since shipping can so easily occur from factory to retail, stores carrying a variety of items may never get one big shipment, just smaller ones directly from manufacturers, reducing middle-men, making it possible for the producer to get more profit while the consumer pays less.

Beyond The Grid

At the stations on the edge of a grid will be zipcar-like rental vehicles. We like small electric vehicles like Arcimoto, because they are as similar in economy and efficiency to Skytran as is now practical. The station will provide charging stations for electric vehicles. But we also want to have available for rental, vans for taking that once a year Ski Trip that you thought you needed to buy an SUV for. (More than 2 people need to take more than 2 pods in SkyTran but with a videolink between them, you're not disconnected.). Pick-up trucks and UHaul like moving trucks will also be available at some stations to further reduce the need for owning and driving such inefficient vehicles.

Greenhouse Gas Target

Reduce the Greenhouse gas now emitted by all forms of transportation in the US by 50%.

Why: Rationale for the proposal

Why not Mass Transit?

Most people travel by car because public transit is so inconvenient. It only has a few stations. When you get there you must wait for the next bus/subway/plane. Mass transit doesn't operate 24/7 so that limits your options. You don't get your own private space. PRT has none of these limitations.

Why Not Cars?

With Skytran, the inconveniences of cars vanish: No need to buy one, find parking, keep quarters for the parking meter, get parking and speeding tickets, shovel the driveway when it snows, wait for your road to be plowed, HAVE a driveway or a road, have a driver's license, car insurance, go to the gas station, change the oil, brakes, etc. fix it when it breaks down, belong to AAA, get in an accident, miss work when it won't start, negotiate with car salesman over trade-in value. The lowest estimate for car costs is 50 cents per mile (see AAA). At 15K miles per year, that's $7.5K per year. SkyTran at 10 cents per mile is only $1.5K for 15K miles.

Much land area is taken up by cars: Roads, parking lots, gas stations, repair stations, inspection stations, auto-parts stores, DMV (division of motor vehicles). Think of the land area taken up by a mall's parking lot. Skytran stops could be INSIDE the mall, with several stops within large malls. Useful buildings could be significantly closer together decreasing the need to travel as far.

Pods are electric vehicles but they are more efficient than any electric car can be because they don't have to carry a heavy battery and they don't have to take up frontal area, volume and the extra weight to protect the passengers.

Why 2 Seater Vehicles

Most car trips contain only 1 person. Comparatively few contain more than 2 people. Why haul around all that extra machinery wasting road space and energy?

Why Tandem and not side-by-side?

Most of a car's energy when traveling over 25 MPH is used pushing air out of the way. By reducing the frontal area, we reduce aerodynamic drag. The SkyTran pods are designed not just to minimize frontal area, but to have as aerodynamic shape as possible and still contain two seated adults.

Why Mag-Lev? Hasn't that already been proved bad for trains?

Mag-Lev reduces the rolling resistance of tires making the pod more efficient. It also reduces the wear and tear that tires and roads exert on each other and thus reduces maintenance costs. (Particles from tires are a significant source of air pollution.) Mag-lev gives a very smooth ride, smoother even than a pot-hole free road. It also allows for switching from one guideway to the other with no moving parts which makes the switching fast and reliable. Mag-lev trains are heavy and thus require a much more expensive track and mag-lev system.

Why Ultra-light Vehicles? Isn't that unsafe?

A pod weighs 200 pounds. (contrast that with 2000 pounds of a car) They are built of composites. Unlike electric cars, they do not need batteries because they get their power from the guideway. They do not need lots of structure to protect the passengers because they move on a computer controlled guideway. We don't say accidents are impossible, but FAR less likely than on our chaotic roadways. Being light, there is much less energy needed to accelerate the pod. The track also has regenerative braking that is about 85% efficient. (The Prius has regenerative braking that is only 50% efficient and it has to stop many times per trip due to traffic lights, etc vs ONCE for PRT.)

Why hang the pods beneath the guideway and not on top?

Hanging below the track in a slot makes derailment nearly impossible. It also allows the pod to "swing out" when going around corners, making a more comfortable ride for passengers and reducing track stress. Since the only exposure the working part of the track has is a slot a few inches wide on the underside of the track, snow and debris won't collect on the track. No snowplowing, street sweeping or pot-hole fixing expense!

Won't the electricity used to power the pods just cause pollution elsewhere?

First, SkyTran is more efficient than any practical near term transportation I know of. At 100Wh per vehicle mile, it consumes the electricity that can be provided by 2 foot wide solar panels on the guideway. This will add to the initial capital expense, but reduce operating costs. Imagine a transportation system that uses NO external energy!

How: Feasibility of proposal

There exists a prototype of SkyTran at NASA's Ames research facility in Silicon Valley. It was paid for by a US Department of Transportation grant that was enough to build a prototype of the pod and 40 feet of track. The Pod can travel down the track at a slow speed under mag-lev.

The next stage is to build a short loop of track, say 1/4 mile with a station and an operational pod. Estimated cost is $20M. That 'test track' should be used both to prove engineering details as well as attract city politicians and activists to a prototype that they can ride in and get a realistic feel for SkyTran. After that, one city needs to get say, 10 miles of track in a loop where the system can be proved with public riders. We expect that once such a city loop is installed, the system will get plenty of orders and be sustainable.

We suggest that the initial $20M come from a government loan. That loan can be paid back from a penny per passenger mile "tax" for the first 2B passenger miles. Once in production, SkyTran's primary cost is $10M per mile for the installation of the track (including a station and pods). This is significantly cheaper than a highway, or light rail. Subways and high-speed rail can cost more than $100M per mile.

That first 10 miles for the first city will likely cost double. We propose the government back a loan for $200M to reduce the risk for that first city.

Since the fundamental technology has been proved and detailed cost estimates have been computed, we believe there are just two remaining likely risks for the success of this system.

1. Will people actually ride it instead of drive their cars?

First, if the system merely replaces existing mass-transit, it will save cities money and give passengers a faster, cheaper, more pleasant experience. But for car drivers, the love affair between a driver and his car in America is legend. Will they give up their cars? First, see above for all the disadvantages of cars. Second, we believe the love for technology has already moved from cars to computers and cell phones for most people under 40. Some of the rest were into cars in their youth but now no longer spend their Saturday afternoons cleaning carburetors. Even older folks will appreciate not having to drive at all. For the die-hards, we expect go-cart tracks and video driving games to flourish. Maybe Indianapolis and Daytona can open up their speedways to armatures between races. With my proposal of covering 50% of the densest part of the population, we only need to cover 3.6% of the land, leaving 96.4% of the land available for car lovers. Undecided? Live on the edge of the network and take the PRT to town and use your car in the country.

2. Will the status quo prevent change?

Despite the US theoretically being a democracy, large issues like transportation policy are decided by a tiny minority of citizens. Big oil, auto, rail, and plane are always resistant to change because there is chance that they will not be on top with a new infrastructure. They control the US government, whose primary role is to preserve or enhance the power of the status quo. Because of this reality, one might conclude that a change in infrastructure as beneficial as PRT is impossible.

Yet change does happen, even to the transportation infrastructure. We have made transitions from walking to boats (esp canals) to horses to trains to cars to planes. Each of these transitions threatened the status quo yet each occurred anyway. One might argue that we are more entrenched than ever, but we can also argue that the incentives for switching to a decent transportation infrastructure have never been greater. At what other time in history did the existing transportation infrastructure threaten the very viability of the planet as a whole?

Though large near-monopolies will perceive PRT as a threat, visionaries within these organizations do exist and occasionally get listened to. For big oil, which already claims to be in the energy business, there's solar panels to manufacture. For Detroit, there's a brand new kind of "car" to manufacture. For rail, the PRT guideway becomes the "smart" rail of the future. For planes, there's an aerodynamic new vehicle to help design and build that "flies" on mag-lev. For NASA, there's a project that will give taxpayers more bang for the buck than any Moon or Mars shot and thus justify their existence in these tight budget times.

We do not require all dinosaurs to change for this transition to occur. We just require enough to slow down their competitors' graft-advantage enough, to permit this transition. Visionary corporations will have plenty of help from politicians seeking new manufacturing jobs in their locale, environmental activists, anti-(oil) war citizens, the poor, small business able to get products to market easier and, once they understand the consequences, 300 million Americans that just want to lead a better life on a planet that doesn't self-destruct.

Vision of the future under this proposal

Your house is cheaper because it doesn't need a garage or driveway. It doesn't even need to be on a street so your taxes can be lower. Because transportation is so fast and cheap, living further from the city is reasonable too and thus land is cheaper so that also brings down the cost of housing. It is safer for your kids because there are no cars whizzing by. When they become old enough to drive, you don't have to worry about drunk driving accidents because they take the PRT instead. It could be closer to other houses since roads and parking aren't necessary, but you might also choose to live further from the city and/or work because transportation is so fast and cheap and you like space from your neighbors. But if you like city life, you get a much quieter, cleaner, safer city where more activities are within walking distance since cars don't take up so much land. Biking is a breeze with no cars to contend with. Negotiation with your spouse about where to live (closer to my job or yours?) is less of an issue and you're less likely to need to move if you change jobs. Between jobs? Life is cheaper so it is not as much of an issue. You're healthier because you're not breathing polluted air and not getting into car accidents. Your health insurance is cheaper because less people need health care. You don't have auto-insurance because you don't have an auto. You do a little more walking and bike riding so you're thinner and healthier. Since you're never stuck in congestion, road-rage is a thing of the past. You can work while commuting, paying your full attention to talking on the phone, texting, emailing etc because you're not driving.

There are no school buses because the PRT network transports the kids. There's a station INSIDE their school. Mothers don't feel the need to drive even young kids to school because they can plop the kid in a pod, punch in the school and rest easy that the pod won't stop until it arrives. It is literally safer than driving the kid to school, faster, and there's no "bus to miss". No school buses saves expense. So does not having to have a parking lot at the school or the snow plows to clear it. (Teachers get to work on the PRT too.) University students not only don't have cars, they find it fast and convenient enough to take classes at other schools. Even in Boston where there's a subway, the PRT is enough faster that the Boston College student wanting to take that MIT seminar doesn't have to waste 2 hours in transportation. Transportation between the 5 colleges in Western Mass is no longer an ordeal. You can even be registered at Hampshire and attend that Harvard lecture in an afternoon. Even a class at Columbia in NYC isn't out of reach for the Boston University student. You could even go to a Broadway show and get home by 1AM without the hassle of LaGuardia or the fear that you'd miss the last flight.

Terrorism isn't common at bus or train stations in the US but ask someone from London or Tel Aviv. Since PRT distributes its passengers in small pods and small stations, there are no large concentrations of people to blow up. There is no security for that trip to the next city either since, well, there's no plane to blow up. The system remembers who went where-when but that information is protected by court order made available only if necessary for solving crimes. There are no parking violations, or speeding car thieves  resulting in a reduced need for police. The police don't need to control traffic at road constructions because there's very few road constructions since most people don't use roads so their load is light. Road infrastructure is less necessary. Taxes go down.

Maybe this isn't enough to stop Greenland from melting all by itself, but it helps. The US is probably economically best place to start, but it can easily spread to the cities in Europe, Mexico, Brazil, India and China. You relax knowing that you're not so much part of the problem anymore. 

A day in the life

You wake well rested in your home in the burbs because its so quiet and the air is so clean. You ride your bike to the PRT station a half mile away and park it in the bike rack. You walk up the 1 flight of stairs and get into a pod, no waiting. You touch your wallet to the screen and it identifies you. Since you are getting on during a weekday morning at the stop closest to your house, the default location is your work. Do nothing and that's where the PRT takes you. Billing is automatic. During the ride, you can use its computer or yours to browse the web, sleep, or whatever. If you're asleep, you're awakened when the door opens at your stop. You walk down stairs, touch your wallet to a bike-share bike and ride another 1/2 mile to your work. On the way home you go via the supermarket, which has a stop inside. You don't buy more than you can carry. But since its so easy going to the supermarket, you don't feel the need to fill up that SUV with bags on that once-a-week shopping trip.


The prototype pod at NASA Ames

A movie of the prototype Pod at NASA Ames moving down the mag-lev track.
(Note .wmv file format might not display in all browsers.
Try Internet Explorer if it fails on your browser.)

Artist rendition of a station. Note the roadway freed up for a pedestrian mall.

Artist rendition of a guideway containing optional solar panels.
Artist rendition of a station with an elevator for handicapped access.

Artist rendition of two guideways crossing at right angles.
Note: this picture lacks a ramp that would connect the two guideways.

Artist renditions of a city before and after SkyTran installation.
In the 2nd picture, a station is embedded in the second story of the brick building.
Wires can be hidden inside the guideway to reduce visual clutter.
We can also plan for the poles holding up the guideway to perform double
duty in holding traffic & parking signs, street lights and traffic lights
to keep pole clutter down.


SkyTran details:

The comments to this proposal contain a set of probing questions with answers that detail the technology, the economics and the benefits.

Transportation statistics:

Personal expenditure statistics:

Urban land area for automobiles:,Parking,CitiesJUPD.pdf

Postscript on Other Proposals

I believe we need to do lots of things to help the economy and the environment. SkyTran is low hanging fruit, but it should be adopted in addition to other solutions, not in place of them. This proposal references directly bike sharing and efficient electric cars, which can operate synergistically with PRT. Those cars need solar cell studded garages to be charged without drawing on grid power. We need more efficient buildings and better water management as well. But none of these technologies may get adopted if we don't have a better process for making decisions, so I fully support initiatives for a more deliberative, inclusive democracy. And the first proposal that such a more collaborative government should take up? Our transportation infrastructure!


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Judges' Choice
Proposal Summary
Personal Rapid Transit grids
Team Proposal: Only team members will be able to edit this proposal. 
By:  fry
Contest: Contest 2011: National
How should national economies evolve through 2100, given the risks of climate change?