There’s very little I do know about in the world, but computer science and mass transit happen to be two things I like to consider myself at least somewhat knowledgeable about. There may be lots of reasons why cars are better than transit in lots of situations, but the analogy to packet and circuit doesn’t convey any of them.

The first PRT project is now underway at Heathrow Airport. A second project has built a test track in Uppsala, Sweden and will soon undertake a rigorous testing program with multiple vehicles. The Masdar Initiative eco-city project in Abu Dhabi plans to provide a PRT circulator system for its auto-free, zero-carbon, new city.

I’ve collected a lot of information about PRT and its available at: http://faculty.washington.edu/jbs/itrans/prtquick.htm

Door-to-door at both ends is certainly desirable. One such innovative system is being developed in Denmark. It is called RUF and is know as a dualmode system (vehicles can be operated on an automated guideway as well as on conventional streets). http://www.ruf.dk is their website. Other dualmode systems are under development and can be viewed at my dualmode webpage: http://faculty.washington.edu/jbs/itrans/dualmode.htm

Perhaps one or more of these technologies could help the Atlanta region work its way out of the transportation mess that I read about from time to time. I’m looking forward to your 2nd article and hope that you can find some time to examine and assess PRT and dualmode as possible transportation solutions that are badly needed in our cities and others around the world. MASS transit is not the answer for the dispersed metropolis. Millions of additional personal autos, no matter how green, aren’t either.

Like circuit-switching, car travel takes a passenger from point-to-point directly. If the infrastructure is massive enough, it’s the highest-performance option. Like circuit-switching, it’s also inherently inefficient and expensive.

Like packet-switching, mass transit takes a passenger through a number of pre-planned, interconnected routes, mostly stopping in places where the passenger doesn’t actually want to be. Although it’s lower-performance, more complex and less reliable than point-to-point transport, it makes more efficient use of whatever infrastructure is available.

That’s why packet switching is popular and circuit-switching is unpopular. Not because packet-switching is inherently higher-performance (it’s not) but because it offers better bang for the buck.

Transportation and telecommunications are probably different enough that this sort of analogy is of little use either way, though. The transport problems we face are hardly abstract ones. Why bother with analogies?

Choose:
-Buses or cars
-Mainframes or PCs
-’5 year plans’ or the free market.

The most powerful of the mathematics is statistics. Einstein was wrong, God does play dice with the universe and
laughs the whole time at ponderous central planners.

“Ride ze fucking subway or ve vill send you to ze Gulag” is inherently funny.

So the equivalent in car terms would be that when the queue at the traffic lights gets too long vehicles are randomly selected, dragged to the side of the road and put through a crusher. I would suggest that if this was implemented, congestion would cease to be a problem quite quickly, particularly since logicaly the crushing would include all the contents of the package. there might however be other problems and I am sure there would be many objections.

OK, leaving aside the unworkable aspects of that, if you can’t drop packets, you must prevent them being sent. By maintaining the traffic in the most congested part of the network just below the point of collapse you maximise the traffic through it. If the traffic gets too high you get gridlock, or the electronic equivalent. So a more workable concept might be that you notify the system of what you want to do and it then tells you when to leave and which route to follow. Perhaps to allow for contingencies and emergencies such a system might allow you to bid for a slot at a higher price, in much the same way that an airline ticket purchased in advance is likely to be cheaper than one bought just before departure. Implementation of this would not be easy, since not only would it have to allocate capacity for planned trips, it would also have to reallocate on the fly to work around problems in the network, such as accidents, traffic light failures and so on.

I also doubt that many would be happy with a system that would at times effectively tell you to forget it when you put in a request to make a trip. Although it could be argued that the congestion at times is effectively telling you the same thing.

I’m interested in your suggestions. Some policymakers have privately emailed me asking for more discussion, so this may not be an entirely theoretical exercise. (Since it isn’t obvious to some visitors to this blog, ‘academicvc’ and ‘stephen fleming’ are one and the same… that’s me!)

Your claim of “more efficient” is only valid if the value of time for the package/person being transported is zero.

Note that for packages where time is important, there are courier services that do indeed carry one box per vehicle.

Most boxes don’t care if they’re locked in little windowless trucks for most of a day. People do. At least, I do. I value my time highly, which is why I value my personal transportation flexibility.

(Same is true in Atlanta… if I want to go from BellSouth’s Midtown office to the airport, I’d be a fool for not using MARTA. From my office a few blocks away, it’s a tossup. From most offices in the suburbs, using MARTA adds significant hassle and delay compared to just driving to the airport.)