10
Dec

2009

What about PRT?

Post by Steven Dale

Personal Rapid Transit (PRT) is a theoretical transit technology, the theory being that in order for public transit to compete with the private automobile, it must mimic the attributes of the car.

Just like a car.

Just like a car.

PRT is typically imagined to have the following attributes:

1. People ride in personal vehicles of up to 4 people.

2. Vehicles are available on-demand.

3. Vehicles travel (typically) on a network of elevated guideways.

4. Off-line stations mean there is no need to stop at intermediary stations or transfer between lines.

PRT is admittedly appealing, but I think it’s mostly smoke-and-mirrors. The technology’s embrace of off-line stations is also admirable, but somewhat misguided. The appeal of off-line stations is that vehicles don’t need to stop at intermediary stations, thereby increasing overall travel speed. The trouble, however, is the need for a huge fleet of self-propelled vehicles to accomplish this feat. To achieve the same result with current rail (or maybe Cable Propelled Transit) technology, one would only have to mimic (and reverse) a technique used in 19th century known as coach slipping.

Coach Slipping.

Coach Slipping.

Could PRT be the transit technology of the future? Sure, why not? I try really hard in my work not to be partisan and if PRT were successfully demoed I’d be the first to jump behind it. After all, I’m the guy that thinks we should commute to work in ski lifts.

Trouble is, PRT has never actually been demonstrated. The idea is over 50 years old and it has never once been implemented. Systems at the University of West Virginia and London Heathrow call themselves PRT, but are in fact, not due to their lack of network capabilities. They are really, just small vehicle people movers.

Some day, PRT may happen and, if so, great. But I doubt it. After all, we already have Personal Rapid Transit. We just use the terms “cars,” “feet,” and “bicycles” instead.

What do you think? Is PRT the technology of the future?

Creative Commons image by Skybum



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Comments

  1. @ Steven: “Trouble is, PRT has never actually been demonstrated. The idea is over 50 years old and it has never once been implemented.” Trouble is, PRT has not only “actually” been demonstrated, it's been successfully demonstrated. One, perhaps the most successful, CabinTaxi, http://faculty.washington.edu/jbs/itrans/cabin.htm, a unique over-under effort that the German government put hundreds of millions into in the 70's, performed flawlessly for a decade. A derivative, CabinLift, http://www.youtube.com/watch?v=F8JDp8uMcO0 links two hospitals and has been running for more than 30 years. There are PRT systems presently in operation at London's Heathrow and Masdar City. And the idea is catching. http://theenergycollective.com/tbhurst/50376/masdar-city-s-prt-catching-ride-driverless-electric-vehicle There are a lot of reasons why PRT is what gondola can only wish.
  2. The idea is not catching. The London system can barely be called PRT while the Masdar system has been scaled back to a point that it can barely be called transit, let alone Personal Rapid Transit. It now basically consists of two passenger stations, nothing more. It's a glorified People Mover. For all the promises PRT makes, it never realizes them. PRT has an awful habit of over-promising and under-delivering. As for gondolas, I never claim them to be the best, brightest, cheapest, fastest, whatever. I don't engage in techno-zealotry. Gondolas are what they are - and quite good at what they do. But I don't over-promise, I merely state what they can do, find examples to demonstrate it and sometimes engage in admittedly theoretical applications of the technology.
  3. What I find interesting is that anti-PRT people always use the same arguments: "There's no real PRT in existence." And when you show them one or two, or three, it's always: "That's not a real PRT. It only connects two or three stations, so it's just a glorified people mover." OK fine. Then I have the same thing to say about urban gondolas. There's no such thing. The ones that do exist are point to point, glorified people movers. Show me a working, high capacity, fast, networked urban gondola in operation and I'll give it a serious look. Until then, I'm more interested in PRT.
  4. The issue is twofold: 1. The PRT lobby always claims PRT to be able to large amounts of people over huge networks of lines with dozens of off-line stations and completely private vehicles. That is, by definition, what PRT is. PRT has never been able to demonstrate that. 2. Urban Gondolas and CPT is not defined by the size of the network, nor off-line stations, nor completely private vehicles. We've never suggested urban gondolas as a replacement for all other transit forms. We suggest it as one of many tools, a complementary system. You need only look to Medellin, Caracas, Algeria, Portland, Telluride and NYC to see that urban gondolas very much do exist. You can't have it both ways: You can't define your technology as some massive improvement over all others but never actually have a working demonstration piece. We don't claim gondolas to be a mass improvement over all other things. It simply is what it is. And what it is, demonstrably exists. That's the difference. You've chosen to define an urban gondola as a "working, fast, high capacity, networked" transit system and you'll give it a look: We've demonstrated on this site how the average speed of a gondola is comparable to existing standard modes. We've shown that gondolas are more than capable of meeting the moderate capacity needs of bus and mid-range LRTs. We've shown that they do, indeed, "work." The only thing maybe we've never shown is that they be networked. But what does that mean? Does that mean they are networked with each other? That they allow line-switching? Off-line stations? If not, oh well, because that's not the definition of the technology. At the same time, we've shown the technology to be fully-capable of full-integration will all other modes of public transit (subway, bus and tram/LRT). You certainly don't have to consider urban gondolas, but to deny them is like saying the sky is green.
  5. I have never thought that PRT was a replacement for other modes of transit. I have always considered it a complimentary, last mile mode, as do most PRT companies. They may suggest that in certain situations, that PRT might serve as the only form of transit needed, but urban planning would have to take that into account as part of the design. I never used the words 'massive improvement', so I don't know where you're getting that phrase. There are certain applications for PRT that are hard to match by any other mode of transit, just as there are certain applications for CPT that are difficult to match by any other mode. By networked, I mean that the system should be able to offer multiple routes to a destination to offer shortcuts (to reduce time in transit) and to bypass problems in the system (broken down vehicles or pods or gondolas). I have yet to see a gondola system that offers this level of flexibility. I am aware of CPT and am familiar with some CPT implementations, but I still have a lot to learn. Based on what I know and what I have seen demonstrated, I am still convinced that in certain instances, PRT would give CPT a run for its money. You are right about one thing, PRT has yet to be demonstrated in a full, networked implementation. But it should just be a matter of time. CPT is good for some situations and PRT is good for others. I don't deny urban gondolas as an option, I just don't agree with the denying of PRT as an option. Incidentally, the CPT system in Portland is a perfect example of my point. It was the ONLY practical option to use considering the landscape. But it only connects the top of the hill to the riverfront. If the system were as practical as people claim it is, they would have extended the system farther afield. They didn't because it costs too much money compared to the trolley system currently serving the riverfront through to the downtown core. So the Portland example does not offer any of the features possible by PRT. I can't speak to the others as I am not familiar enough.
  6. "By networked, I mean that the system should be able to offer multiple routes to a destination to offer shortcuts (to reduce time in transit) and to bypass problems in the system (broken down vehicles or pods or gondolas). I have yet to see a gondola system that offers this level of flexibility." Pot calls the kettle "black." PRT has never demonstrated this degree of flexibility either.
  7. I believe I already said that. Read the whole response. Now that we have that out of the way, PRT does have the capability to do it. In fact, to a very small extent, this capability already exists at Heathrow. Plans are still in place to expand both the Heathrow network and the Masdar City network.
  8. Again: To a very small extent, this capability exists at Heathrow. As for your plans at Masdar . . . Have you looked them up lately? Masdar's basically dead in the water. It's now a point-to-point, 2 station people mover. Doesn't quite live up to all that PRT presupposes it to, does it? My problem with PRT is that it over-promises and under-delivers - for the last 60 years. When it comes to CPT, we're not promising much more than a cost-effective system to solve last mile problems with LT1M wait times. Nothing more. CPT has proven itself capable of solving that problem. PRT hasn't been able to prove it after 60 years.