PRT-- Unproven?

"PRT is unproven"-- or is it?

November 2001. Perhaps the most powerful argument in the anti-Personal Rapid Transit arsenal is "PRT has never been tried." Transit agencies which have selected light rail or monorail technologies as their preferred technology dismiss PRT has 'experimental', 'untried', or 'unproven'. "Get back to us when PRT has been proven," is the usual excuse. But the parts that make up PRT have been proven, although separately and over a period of many years.

Network guideway	Elevated rail configured in a network, as opposed a line-haul corridor, is not new. CVS, a Japanese PRT demonstration, successfully operated small automated vehicles on 2.9 miles of grid-configured guideway in the early 1970s. The Group Rapid Transit system at West Virginia University, built in 1974 and still in operation today, has 8.7 miles of guideway. It operates over 70 vehicles among 5 stations, carrying an average of 14,000 passengers per day.
Test track	"We won't be convinced until you build a PRT test track" is another excuse for not going forward with PRT. In fact, there has been a PRT test track, and recently. One was constructed in Massachusetts for "PRT2000", Raytheon's system based on Taxi 2000 concepts. It proved the core features of PRT are feasible: computer control, multiple vehicles, in-vehicle switching, short headways. Unfortunately, it also proved another central PRT tenet: that if you make the cars too big & heavy, then you have to make the guideway structure big & heavy, and everything gets too expensive.
Short headway	Operating vehicles close together is needed to maximize the number of vehicles per unit of time, but doubters question whether short headways are possible. Raytheon was not the first time short headways were proven, succeeding in reaching 2.5 sec. headways at 30 mph for PRT2000. In the 1970s Cabintaxi, a German PRT project [ Video ], had achieved 0.5 sec. headways. In the 1990s the National Automated Highway System Consortium succeeded in operating a platoon of automobiles on a freeway at less than a 1/2 second of separation. Table
Control software	In a world where the poster child for computer glitches is the tempermental Windows PC, the anti-PRT faction questions whether it is even possible to write code which can control a PRT system, reliably and safely. But this is not impossible. Taxi 2000's code has been tested successfully many times in various applications. Raytheon wrote its own code for PRT2000, and that also worked successfully on its test track. FROG, a Dutch maker of control systems for amusement park rides and cargo mover systems, is supplying the control and navigation system for ULTra.
In-vehicle switch	The switch, to be mounted in the vehicle undercarriage, is the only component invented specifically for Taxi 2000. It is patented, and has been tested successfully in the PRT2000 system.
Lightweight vehicles	Some doubt whether the PRT promise of a lightweight small vehicle is possible. Recently, Taxi 2000 has estimated its car will be about 1,000 lbs. Transit agencies ask consultants to make guesses about PRT vehicle weight and the guesses are always high, on the order of 2000 or more pounds. Who's right? Consider the popular Smartcar, a European minicar made by a Chrysler subsidiary. The Smart weighs in at 1600 lbs. and, at only 2.5m long (8.2 ft), is about the size of a Taxi 2000 vehicle. Imagine stripping the Smart of the parts needed for road use: metal wheels, axles, engine, drive shaft and differential, suspension, transmission. What's left are the seats, frame, windows, and plastic-composite body panels. The weight is going to be far under 1000 lbs., even when adding back some weight for the PRT undercarriage. And by the way-- the Smart only costs about $8,500.
Propulsion	Propulsion and braking in a PRT system like Taxi 2000 will be performed by electric Linear Induction Motors mounted in the vehicles. LIMs are basically rack and pinions that operate through electromagnetic repulsion instead of mechanical teeth: a vehicle-mounted LIM uses magnetism to push along a passive steel guideway. This eliminates the need for transmissions, bearings, gear boxes, etc. and removes the problem of maintaining adequate traction between wheels and rails. This lack of moving parts within the LIM reduces both the need for regular maintenance and for emergency repairs. LIMs are far from exotic technology, and are commonly used in applications such as conveyers, sliding doors, rollercoasters, airport people movers, and even mass transit-- used since 1986 in the Vancouver Skytrain rail system.

This is what we mean when we say that PRT is based on proven engineering and construction methods, and the use of off-the-shelf, non-exotic components. PRT merely proposes combining them in a new way.

We are only left with the objection based on the chicken-or-the-egg dilemma: 'We won't build PRT until someone else builds PRT first.' In recent years many advances in microcomputers and lightweight plastics have occurred, increasing PRT's technical and cost feasibility. So the standard objection has been changed to 'We won't build PRT until someone else builds one first AND it is proven in transit applications'. With this circular reasoning working against it and the bar being raised, PRT can never happen, seemingly. But it is happening. The British government and the county government of Cardiff, Wales, has financed the world's second modern PRT test track, for the ULTra system. All indications are that an ULTra system will be up and running in fare service in Cardiff by 2003.

PRT will then be unquestionably proven.

Here is the choice for transportation policy in Seattle:

Do you build a multibillion-dollar train system which won't reduce congestion?
Or do you select PRT: cheaper to build, able to pay for itself through the farebox, and more likely to reduce congestion because of its accessibility and on-demand & nonstop travel?

Which do YOU think is the more fiscally responsible course of action?

Get on board! Personal Rapid Transit

The author has a degree in Policy Analysis from the University of Washington Graduate School of Public Affairs (now known as The Evans School).

Sample Headway Table

Short headways sound safer expressed in distance rather than time.

Seconds	Speed (m.p.h.)	Tail-to-head Separation	PRT car lengths Approx.-- 9 ft/car
2.5	35	119.3 ft	13.2
2.5	30	101 ft	11.2
1.0	35	42.3 ft	4.7
1.0	30	35 ft	3.9
0.5	35	16.6 ft	1.8
0.5	30	13 ft	1.4