Public Transportation and Smart Growth

and no city in the world has ever adopted it as the basis of its transit system. Sure, various cities have individual, limited lines, but no city has a multi-line system that covers even a small area.

Do you know why?

I once talked with a local PRT advocate, and I was able to leave him speechless. Here's why:

Do a thought experiment.

Think of a city with a fully functioning PRT system, let's say trunk lines in all four directions radiating from the downtown area and branch lines into neighborhoods. Now think of rush hour. Thousands of people leaving downtown and getting off at various stations. How do you avoid backups with only one track in each direction? If you have "off-ramps" for the stations, how do you prevent backups at the off ramps for popular stations? What about backups at the on ramps to enter the main flow from popular stations? Once the people get home, you have a surplus of pods at their destinations that may not be needed till the next morning. What do you do with them?

Suppose inbound a bunch of inbound pods are making their way downtown from Mile 10. There are a bunch of people at Mile 5 Station who need to get to work, but all the pods are taken. What do they do as e pods pass them by? Do they flag the first empty one down electronically? If there's no off ramp, just one track, that means holding up the full pods from Mile 10. If there is an off ramp, how can the people in the station see that there's an empty one?

Note that a train (like the exemplary commuter systems in Japan) runs back and forth on its schedule, whether there are passengers or not. It meets a schedule and stops at each platform for a predetermined amount of time. No one gets left out.

Then there are the stations themselves. The sketch shows them with room for one person, with the station accessible only by stairs, which would make it awfully hard for the guy with the stroller to access it. Building stations with elevators and room for a lot of people to wait raises the price tremendously.

PRT works only when there's a single line with few stops. Adding extra lines increases complexity and raises issues that I've never seen a PRT advocate answer.

The biggest advocates of PRT are Republicans who want to waste transit money on systems that don't work but have the superficial appeal of letting white flght suburbanites imagine that they can enjoy convenience without encountering the people whom they irrationally fear.