Personal Rapid Transit: "...computers are not the magic bullet that will save us."

From the Minneapolis Issues:

Ignoring all of the problems with actually building the [PRT]
infrastructure, I will focus in on the area of my professional
expertise: large-scale computing systems.

The idea that computers can automatically control a distributed
network of machines that by their nature have a human interaction
component and that this system will work at peak efficiency
with vehicles traveling inches behind one another is absurd.

We have plenty of examples of much smaller and less complex
systems have taken years to get right, if at all. A few that
come to mind:

- Denver airport's baggage handling system

- MSP airport's trams (which only go from one single, fixed point
to another!)

- Metro Transit's GoTo card system

As a computer professional, I can state with utter certainty that
computers are not the magic bullet that will save us. At one
level they are extremely simple machines. But at another level,
they are incredibly complex. Debugging distributed software is
no easy task. Programs will always have bugs. The question is,
can the developer get rid of enough of the critical ones to make
the system mostly functional? Is mostly functional good enough?

In technical terms, the problem of optimally scheduling a
distributed network of traveling objects is likely NP-complete
(I haven't done the formal analysis). That means that the
computer will have to make guesses and I can guarantee that
it will guess wrong in some cases. That doesn't mean the
system will break down, but it won't always achieve the peak
efficiency that its promoters proclaim.

A system like PRT will need many layers of redundancy, and that
adds cost. I just don't buy the claim that private companies
will pay for it and make a profit. If that were the case, why
does PRT need any subsidy at all?

I work in the supercomputing industry developing the software
that users need to develop their applications. I also do some
high-level hardware architecture work. A system like PRT will
need something equivalent to a low-end supercomputer to work.
I know how difficult it is to get these systems to function.

The claims made by PRT proponents are pie-in-the-sky nonsense.
They are made by people who have no real understanding of the
underlying technology needs and complexities.

David Greene
The Wedge