Saturday, August 9, 2008

3> First, there is the track

First there is the track. This is the most important part, and is half the reason the world needs to “open source” PRT design. I have not seen a single PRT system that I think will ever find any success in the U.S. and here is why. PRT can not compete with buses or light rail in situations where people can aggregate at a point A in order to make a straight line journey down a main drag to points B, C, etc. It is simply inefficient to load and transport many small vehicles as opposed to a few large ones.
As we all know, however, mass transit has real problems competing with cars because it can’t effectively reach less trafficked areas. Yet many people are coming from a less trafficked area, and are destined for a less trafficked area, and are effectively forced to commute through highway and intersection bottlenecks. Mass transit though these bottlenecks is unworkable because there is no infrastructure on either side of that bottleneck that would enable a commuter to complete the journey.
The answer is cheap, go-anywhere, go-over-anything, rails, and go-exactly-where-you-want cars to compliment them. We don’t need a couple of loops. We need a network. This is a critical mass situation. The system needs to have more destinations than is practical with the alternatives or else the alternatives should get the funding.
One problem with the current development model is that the companies hoping to build a PRT system covet the idea of the never-ending construction job that would be the track. It is no wonder that they tend to envision more grandiose guide-ways than the needs would seem to indicate. The same is true of the cars. Just like GM liked the business model of producing SUVs, instead of compact cars, so does the potential sole supplier of PRT “pods” covet the endless production of larger, more expensive vehicles.
Here is a picture of the Raytheon’s idea of a PRT vehicle.

PRT 2000

Is it any wonder that the cities that Raytheon approached eventually rejected it? Note the 72” x 72” track size. Clearly minimal cost was not the object here. The use of a 36” horizontal tubular support beam is a particularly odd choice, as ordinary “I” beams are cheaper, stiffer, less resonate, easier to handle, easier to bolt to, and more available.