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An Introduction to PRT
Nov 1, 2009—
With all the news about Measure R money, Stimulus funds, highway, rail, bus and bike projects going on, there's little attention left for emerging transportation technologies with the wide-eyed dream of solving some of transportation's worst woes, such as safety, accessibility, energy efficiency, pollution and cost concerns. Personal Rapid Transit (PRT) is a category of transportation technology that hopes to unite the best aspects of all systems in a new transportation paradigm, a dream many believe is too good to ever be possible. Although LA's own Blue and Red lines are actually designed to be driverless, and only use the human drivers to open and close the doors at each station, it is far short of the ubiquitous, ultra-light, small vehicle rail system most PRT enthusiasts envision.
There's been a move lately away from the term PRT for Personal Rapid Transit, to Personal Automated Transit (PAT), which does indeed better describes what most PRT enthusiasts are talking about. The Advanced Transit Association (ATRA), a collection of the leading proponents of PRT set forth these guidelines in 1988,
- Fully automated vehicles capable of operation without human drivers.
- Vehicles captive to a reserved guideway.
- Small vehicles available for exclusive use by an individual or a small group, typically 1 to 6 passengers, traveling together by choice and available 24 hours a day.
- Small guideways that can be located aboveground, at groundlevel or underground.
- Vehicles able to use all guideways and stations on a fully coupled PRT network.
- Direct origin to destination service, without a necessity to transfer or stop at intervening stations.
- Service available on demand rather than on fixed schedules.
While PRT prototypes and demonstration systems exist, including 2getthere in the Netherlands and PodCars in Sweden, PRT enthusiasts are excitedly waiting for the Ultra system being installed at Heathrow airport to demonstrate the safety, practicality and profitability of PRT.
Many people confuse PRT with MagLev (Magnetic Levitation), since MagLev is a popular propulsion scheme employed (or “envisioned”) by many PRT projects. The two most popular designs are the original Electro-Magnetic System (EMS) used in the larger MagLev trains in Germany and China, and the Electro Dynamic Suspension (EDS), developed by General Atomics. The larger EMS is made to lift heavy vehicles of 6-11 tonnes and uses a nitrogen cooling system, and other mechanisms related to stopping, starting and controlling very large trains. The EDS design employs a few innovations such as placing the magnets in a Halbach array that concentrates the magnetic force on one side, lifting the vehicle in relation to the speed, thus simplifying some of the breaking and “gap management” issues of the EMS design.
Most PRT designs employ wheels and electric motors somewhere, whether or not they use MagLev as well, and the buzz on that front is over in-hub motors, AKA wheel motors, which are wheels with light-weight electric motors built right in the wheel itself, eliminating the transmission and drive train, reducing energy loss, and simplifying control issues (including regenerative breaking, which transforms energy absorbed in one process to provide energy to other processes).
Another popular PRT debate is over dual-mode systems that use vehicles capable of traveling off the guideway, like a bicycle or car, and allow the same vehicle to enter a guideway system that provides faster speeds and greater safety by managing cross traffic. The question is what comes first, the guideway or the cars?
Meanwhile, the dreamers at University of Washington have been updating their web site, and it appears that the billions of dollars in taxpayer transit money is being dedicated to traditional modes of travel have not shaken the PRT enthusiast out of their reverie. Some of us witnessed the PC revolution transform suddenly from an impossible pipe dream to an unstoppable force within a few short years, and we know that when you're coming to the crest of a hill it always appears to be moving away from you right up until the moment that you reach the top.