Personal Rapid Transit



One of the Best Analyses of PRT You’ll Ever See

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We here at The Gondola Project tend to be a pretty open-minded group of individuals with our readership generally following suit. We’re not, however, slaves to fads or trends. When we look at new ideas, innovations and technologies, we try our very best to be objective and analytical about them (but appreciate and love the craziness of things like the Chinese Tunnel Bus™).

We approach things from a position of empirical skepticism. We need to see that something can actually work – or at the very least, that the theory and logic underpinning a concept makes sound and reasonable sense. As a result, we’ve tended not to have a fondness for the mythologized panacea of the public transportation world; Personal Rapid Transit (check here and here for two of our more interesting debates with PRT advocates).

The fundamental logic behind PRT is quite simply flawed with most advocates of the technology blind to the economic and technological limitations of it. But that doesn’t prevent it from being continually trotted out as transportation messiah.

That’s why the work of blogger and researcher Apatzer is so fascinating.

Over at a brand new site called Apatzer meticulously (and sometimes exhaustingly) details the 6 months he spent researching and coding a simulated PRT network to investigate the technology’s feasibility.

His basic findings are that PRT is financially unfeasible; is incapable of providing the needed capacity in dense urban environments; and cannot provide the time savings over the private automobile typically sold by PRT advocates and companies.

I won’t go through his entire analysis as that would take about as long as it took him to do his study. As such, it’s hard for us to say whether his work is “right” or “wrong.” But for anyone interested in PRT as a viable urban transportation solution, they should spend a serious amount of time and energy exploring his work.

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The (Il)logic Behind PRT

The Morgantown PRT. Those vehicles sure do look personal don't they? Image by Brian M. Powell.

Personal Rapid Transit (PRT) is a technology that’s been dreamed about in transit circles for roughly the last 60 years with little to no progress. For those unfamiliar, the concept of PRT is based around the following 4 principals:

  • Small, automated vehicles with seating for 2 – 8 people.
  • Vehicles available on demand at stations throughout the system.
  • Direct from origin to destination. Vehicles do not have to stop at intermediary stations.
  • Non-linear networks of stops, thereby eliminating the need for transfers.

The concept is that for public transit to compete with the private automobile, it needs to replicate the comfort of the car. Fair enough.

The transit-geek-gadgetbahn-aficionado in me would of course love to see PRT sometime in my lifetime. But that’s based upon blind hope and little else. The fundamental logic behind PRT just doesn’t work. Here’s five reasons why:


ONE. Vehicle Capacity. The appeal of Personal Rapid Transit is that it’s personal.

And yet if every vehicle were loaded with only one single rider, there would be plenty of wasted capacity and seats. As a PRT system typically has only one single guideway, the system would basically just be replicating a single lane of under-capacity cars. There is, however, a solution to this problem. Which leads me to my second problem:


TWO. Solving the vehicle capacity problem negates the whole concept behind PRT.

The only way to solve the problem outlined in the previous point is to enforce a ‘carpool’ mentality. How popular is carpooling? Station attendants would necessarily have to force riders to ‘buddy-up’. 8 person vehicles would be filled by 8 people whether they were traveling together or not. Suddenly it’s not personal. Suddenly you have 8 different people traveling to 8 different locations. Which leads me to the third problem:


THREE. Station Attendants will cost money.

Any cost savings that PRT imagines would be erased by the need for station attendents to enforce carpooling during peak hours. Despite having these station attendants, it’s unlikely that the attendant will be able to group passengers according to their destinations. As such, we have a fourth problem:


FOUR. People going in 8 different directions must travel in 8 different directions.

So now it’s rush hour and we’ve got 8 different people traveling to 8 different destinations. Now the algorithm used to control the vehicles must calculate a linear route that stops at each destination sequentially. And that would be utter insanity. Imagine if you and your fellow rider were traveling to destinations at the exact opposite ends of your respective city!

You could solve this problem by giving everyone their own vehicle, but to do so leads us straight back to point ONE. The only real way to deal with this issue is to institute fixed routes, which leads me to the fifth problem:


FIVE. The Appeal of PRT is the Elimination of Fixed Routes.

If suddenly every PRT system is a linear fixed route, then what we have is nothing more than an Automated People Mover that has the ability to skip stations. Note, however, that as 8 different people with (presumably) 8 different destinations are using this souped-up APM, riders will still be faced with the situation of stopping at stations different from their destination.

It shouldn’t surprise anyone that the most famous “PRT” system in the world is the Morgantown PRT in Virginia -which shares a surprising resemblance to the situation I’ve just described.


SIX (BONUS!). Google’s already invented PRT.

It works and is a driverless car.

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Pod Cars Start To Gain Traction

Yesterday, the New York Times ran a piece titled Pod Cars Start to Gain Traction in Some Cities.

The author, Jim Witkin posits this basic question: Is PRT finally ready for prime time?

The article is scant on details but suggests that London Heathrow’s PRT pilot system is evidence that the technology is ready to be deployed throughout the world. Problem is, the technology is no where near “ready for prime time.”

According to the article, the Heathrow PRT system includes 21 vehicles, 3.8 km of elevated track and will carry 1,000 people per day. Per day. For comparison purposes, the Medellin Metrocable moves approximately 40,000 people per day over its 2 km of guideway.

For whatever reason, people love to debate the merits of PRT and the Heathrow system ad nauseum (see the comments on this post for just such a debate). I suspect it has to do with the ideological fervor PRT advocates possess and the natural cynicism that accompanies such fervor.

But absent from much of the debate is this: The Heathrow system doesn’t work.

Construction on the Heathrow PRT was completed in mid-2008 when testing began. Fast forward two years later to today and the system is still not open to the public and there doesn’t appear to be any consensus about when it might be. (A fact strangely missing from Witkin’s article.)

Until this (or any other PRT) system can demonstrate its functionality in a pilot program or other environment, PRT will continue to be nothing more than the public transit technology of the future – a designation its held for the last 60 years.

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Lowered Expectations

If you’re expecting to see urban gondolas and cable propelled transit systems zipping through you city any time soon, I’m here to tell you something: You’re wrong.

Sorry to disappoint you.

Sure, with the right political will and visionary planners, there will be successes here and there, but things won’t change overnight. Things just don’t move that quickly. (Remember as a kid how long it took for Christmas morning to arrive?)

And for cable, that’s a good thing.

Cable’s in an adolescent stage right now. It’s finally stepping into the public transit realm. But to get it right will take time and practice. Better to lower the public’s expectations and win a few, small victories along the way towards mainstream acceptance.

The other option would be to make the mistake PRT has made for the last 60 years: Promise everyone the world and never accomplish anything.

PRT, after all, has been the transit technology of the future for the past 60 years with only minor accomplishments. The only thing more disastrous than PRT’s track record has been the industry’s attempts to manage the public’s expectations.

As they say, talk is cheap.

So let’s lower our expectations: CPT won’t be everywhere tomorrow. It will, however, continue to evolve and make incremental improvements. There’s a good chance the technology will come to your city sometime. But not immediately, and not without your help.

Give it time.

Want more? Purchase Cable Car Confidential: The Essential Guide to Cable Cars, Urban Gondolas & Cable Propelled Transit and start learning about the world's fastest growing transportation technologies.