Monday, September 28, 2009
I have been more and more confused as of late. It seems like there are so many competing visions of PRT, it’s almost impossible to define. A quick look at Wikipedia gives this seven point list compiled by ATRA in 1988.
1. Fully automated vehicles capable of operation without human drivers.
2. Vehicles captive to a reserved guideway.
3. Small vehicles available for exclusive use by an individual or a small group, typically 1 to 6 passengers, traveling together by choice and available 24 hours a day.
4. Small guideways that can be located aboveground, at groundlevel or underground.
5. Vehicles able to use all guideways and stations on a fully coupled PRT network.
6. Direct origin to destination service, without a necessity to transfer or stop at intervening stations.
7. Service available on demand rather than on fixed schedules.
There can be little argument about point one. Point 2, however, seems a bit restrictive. What if you want to detach the vehicle (cab) from the drive unit or bogey? “Why do that?” you ask. Perhaps the payload is cargo, not people, and you want the whole container. Another possibility is that of dual-mode, where the vehicle can drive away. An argument against dual-mode has been that if the vehicle was not well maintained, it could break down and clog up the system. If the drive unit, however, stayed in the track, a vehicle could be carried just like any other piece of cargo. Number 3 is, of course, subject to the previous argument. Cargo can help pay the bills especially in the middle of the night.
As per number 4. How small is small? To me the ULTra track seems like a full fledged road. I think the main thing is a commitment to 3D. (more on that later) Number 5 seems a bit arbitrary to me. My question is why? What is wrong with the possibility of private “spurs” that run into private property? It also seems possible that the track might come in various classes, such as a lighter, tighter turning version for industrial use. The passenger vehicles can obviously be “smart” enough to avoid going on such track. Number 6 and 7 seem fine, although again, one person’s attribute is another’s restriction.
I think it pays to consider that we humans have been largely earth-bound since the dawn of time, so that sometimes we don’t really recognize the nature of the problems it causes. Roads and cars are a 2D solution. Sure, we can build a bridge, or even a cloverleaf, but it’s still basically ground flattened to roll stuff on. Many of the definitions above are basically attempts at overcoming the shortcomings of being stuck on the ground. Isn’t PRT necessary primarily because there isn’t any more ground between point A and Point B? This seems especially true now that battery technology is enabling true electric vehicles. Why not just add six foot “electric only” lanes? Oh, yeah. No room.
Imagine a world with skyhooks, and you’ve imagined a world where all transit is point-to-point, on-demand, etc. The infinite PRT network. I like to think of the problem in terms of XYZ coordinates. Mary Poppins can apparently go anywhere within the atmosphere, but we must be content with the network of track and the capabilities of the vehicles they carry. Never-the-less, the ultimate objective of PRT, as I see it, is to enable a person or thing to be plucked from one place and dropped in another. Everything else is just a means to that end. Looked at in this light, it is clearly imperative that the track be as light and adaptable as possible, for this will ultimately determine how many XYZ coordinates the network serves and, therefore, its ultimate usefulness. In a world of so many competing PRT visions, let’s remember this metric for measuring their worth. We can call it the Mary Poppins test.
Posted by Dan at 7:08 PM