We have a dream: that every large city have a rapid transit system that is an ubiquitous public utility. You wouldn't live in a house or apartment that wasn't on the electric grid, or served by the water, sewage, or waste collection systems, would you? We think there should be the same attitude toward transit access. Wherever you live in a city, you should be able to walk no further than 4-5 blocks to a rail transit station.

The key is the concept of a transit network comprised of many small stations:

Radial vs. Grid
Radial: How is this line-haul train system convenient for someone traveling between the red dots?	Grid: Put the red dots anywhere, and the grid transit network makes travel between them convenient. Transit Grid ©2000 Get On Board!PRT
Transit Grid ©2000 Get On Board!PRT

Subways would be ideal, and we think subways ought to be the core of any serious urban rail network. We acknowledge that Portland has proven that light rail can also fill this central role. But at today's prices, a truly pervasive network with the desired 4-5-block-walk criterion is not affordable.

Enter Personal Rapid Transit pods.

The idea of PRT can be summed up by the analogy "a rapid transit system that works like an express elevator, only horizontal." A large fleet of small driverless vehicles (also called cars, pods, and sometimes capsules or cabins) provide on-demand, non-stop rides, to any other station in a network, as selected by the user when the ride begins.

As with an elevator, a pod ride only happens with someone on board; this has an obvious energy savings advantage. Also like an elevator, there could be as many passengers as allowed up to an engineered weight limit. The only operational requirement is that they all want to go to the same destination station at the same time. Anyone who misses that pod, or wants to go to a different station, can simply use the next one. When the selected destination is reached, the pod is released to serve another person or group.

When a city is deciding to build a subway or light rail system, a consideration in where stations are located and the distance between them is the revenue stream being produced to pay for the system's capital and operating costs. Therefore, the higher the population density around a station, the higher the potential ridership and revenue. An area with extremely high density could even support multiple stations.

But an area with low population density might only be able to support one station, if even that.

The objective with PRT is to create hardware that has a small surface footprint, a low aerial profile and low per-mile construction cost. With less costs to recoup, such a system would be affordable to install in low to moderate density urban areas. Hopefully there would be so many stations that you'd never have to walk more than 4-5 blocks.

The P in PRT stands for Pod or Personal; the on-demand aspect meant service would be personalized to your needs, instead of on a timetable, and choosing your destination meant personalization of the route as well. But in the public perception Personal was often misinterpreted as private like the automobile, and consequently assumed to be low capacity.

While it's sort of like a carshare service, PRT is not a private car. It's driverless, and moves people all day instead of sitting idle in parking lots. Yet it only moves when someone needs one.

It's tempting to see a small transit pod and think it wouldn't have much capacity, but think of it in terms of aggregates. A fleet of transit pods would have an hourly capacity (R) equal to fleet size (N) times the number of seats per pod (n), times the number of trips (T) a pod can make in an hour:

(N * n) * T = R

So for a fleet of 300 pods with 6 seats each, each pod capable of 8 trips per hour,

(300 * 6) * 8 = 14,400 hourly capacity

It's not meant to replace existing transit systems that work well. Although PRT could serve a city that has no rapid transit currently, it could also extend the reach of rail systems that don't go to enough places or have enough stations.

PRT is not slow. Most currently operating systems travel at 20-25 mph, and many people think that's not fast enough. But in an urban setting, 25 mph is plenty fast when the pod doesn't stop for lights or traffic, and doesn't stop until it gets to your destination.

Attempts to build, test and deploy PRT have been going on since the 1960s. One has been running in West Virginia since the 1970s, but there has been more success in recent years because Computers. Today new pod systems are operating at Heathrow Airport, Abu Dhabi's Masdar City, and an ecological preserve in South Korea.

That none of the new PRTs are in the United States is a shame, since it was an American who in the 50s came up with the definition of PRT, the US Government sank a lot of time and money into it in the 60s, and between 1970 and 2011 the PRT in West Virginia was the only one in the world.

What is needed now are federal and/or state agencies that will act as a vetting authority of transit pod technologies. For years American PRT companies have been stuck chasing the elusive first contract in hopes of leveraging private investment capital, and vice versa.

It's a formula the passage of time has proven doesn't work.

What has been missing is an authority, ideally the federal government, maintaining a procedure for evaluating advanced transit companies and their designs, providing a measure of developmental funding for ones that meet the smell test, and administering a roadmap to regulatory certification.

USDOT is the natural home for such a program, and it need not be expensive most years. All that might be required is a staff, a list of experts willing to act as evaluators, and a development & demonstration matching grants program that need spend nothing if it receives no qualified applications.

A significant problem in the American PRT/GRT industry has long been the small and sometimes imperceptible amount of separation between companies with viable technology, companies with some good ideas that need work, honest efforts that don't have a chance in hell, and outright scams. A vetting authority would divide the varieties of wheat from chaff almost overnight, reducing uncertainties for policymakers as well as protecting taxpayer interests.

Unless they're public shared vehicles, we hate them. If you take the misery out of long commutes, heavy traffic and parking, you potentially dilute support for expanding transit and laws containing urban sprawl. On the other hand, fully autonomous vehicles are potentially a flavor of PRT, provided the vehicles are 1) publicly owned/operated by transit agencies, 2) dedicated solely to transit service, and 3) can be treated as virtually grade-separated due to road infrastructure and crash avoidance technology.