monsoon, on Jan 16 2008, 10:18 PM, said:
I don't understand why it is a good idea to move all these vehicles onto a track. It doesn't solve any problems.
If you don't understand, then I will be happy to explain it to you.
The basic reason for the track is that it facilitates automated control - automated solutions that run on regular roads are a much more difficult technological problem, whereas control algorithms for dedicated, segregated guideways are much simpler. In fact, the problem of automated control of vehicles on a fixed guideway is essentially
solved. PRT pioneer JE Anderson has published detailed, peer reviewed academic papers on this topic. It's simple physics.
Roads, on the other hand, have too many variables for an automated system to work. Road navigation is a distinctly human trait that is very difficult and error prone to automate. Sure, we're starting to see baby steps in that direction - self-parking automobiles are an example - but the leap from self parking car to fully automated automobile operating in highway traffic is
huge. We won't see anything like it in the next 20 years, at least. So if you want full automation, you need a guideway. And full automation is the only way to provide automobile-like convenience for a reasonable cost in a public system. Taxis come close - they are a public system that provide automobile-like convenience - but they are very expensive because they require a driver, and therefore only accessible to the wealthy.
A side benefit of the segregated track is that it leaves the street level to pedestrians -which is much safer and would enhance walkability in cities.
You must also understand that a single PRT guideway, even operating at low speeds and moderate headways,
has significantly more capacity than a single lane on a city street. This is because control algorithms can automatically optimize and reroute traffic - there are no stop signs or traffic signals in PRT, because the control algorithms know where every single vehicle is located down to an inch resolution, and can fully utilize every inch of guideway capacity.
Intersections restrict road traffic so much that freeways were introduced into the road network in order to support demand. Because of the lack of intersections, the carrying capacity of a freeway is much higher than a city street, but freeways also have this minor little drawback that they
destroy the fabric of cities. So for the automobile, you have two choices: plain old city streets that are gridlocked because they can't handle all the traffic, or freeways that decimate neighborhoods into oblivion.
So you have a city like Boston which, when faced with the choice of freeways or gridlock, instead chose to bury all their freeways underground - a solution that seemed really innovative until the endless construction problems pushed costs to
absurd levels - tens of billions of dollars!
Other cities try to do it with rail, and have some limited success - but we all know that people in huge numbers will choose their car over rail because of the convenience factor. Rail helps, no doubt, but the automobile still wins by a long shot. Even in dense cities like NYC with great rail networks, auto traffic is bad.
Now consider PRT. A single guideway running at moderate speeds and headways can provide nearly the capacity of a freeway lane while barely touching the street. If the guideway network density is high (a guideway every few blocks) you can achieve the equivalent capacity of a full fledged freeway network criss-crossing the city without
any impact to the street level. Furthermore, parking needs (another huge problem in cities) are vastly reduced because PRT vehicles are constantly reused - and can be automatically stowed away in a remote storage facility when demand is low.
So a well developed PRT network provides the capacity of a freeway, the convenience of a private automobile, no parking requirements, no impact to pedestrians or bicyclists, ubiquitous availability for
anyone who can afford a $1 fare, very low operating costs that can be supported fully by fares, zero local emissions, accessibility for the disabled, and better safety and energy efficiency than any other mode of transportation.
And, furthermore: many studies (even by PRT critics!) have shown that people would be willing to abandon their cars for PRT in
record numbers - some estimate that
30% or more of automobile drivers would switch to PRT for their daily commute. Compare this to other transit options which rarely attract even
5% from their cars.
People, this is not marketing fluff - dozens of independent research groups have studied PRT for 4 decades and have all come to these same conclusions, while nobody has yet disproved a single one of these claims.
Does this answer your question as to the problems that PRT solves?
Edited by TrEn, 16 January 2008 - 10:34 PM.
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