Personal Rapid Transit: A Response to Professor Vukan R. Vuchic
by J. Edward Anderson
Systematic technical analysis by a significant number of groups has shown that PRT is not only practical, but will have outstanding benefits for many urban areas. Vuchic's conclusion that "guided systems are economically justified only when they have spacious vehicles, such as light rail or rapid transit trains" is wrong. Spacious vehicles are needed in conventional transit systems for two reasons: The first is to amortize the wages of drivers over as many trips as practical, and the second is due to use of on-line stations, which block the main line when a train must stop and result in required headways of a minute or more. The spacious vehicles that result require wide rights-of-way or heavy guideways, either of which drives the costs beyond reason for most American cities.
If all stops are off-line and the vehicles are short, the safe line headway reduces to a few seconds even if railroad stopping criteria are used. With proper design, headways less than a second are practical, indeed, the National Automated Highway System Consortium plans to test a group of ten automobiles on an automated freeway at 0.3 sec headway, much lower than needed for operation of PRT systems at a total cost per passenger-mile many times less than experienced with light and heavy rail systems. A glaring inefficiency of conventional rail transit is their daily average load factors of less than 20 percent. The demand-responsive service of PRT is much more efficient.
The comparison Vuchic gives of the inefficiency of automobiles in the center of major cities with PRT is incorrect. Automobiles are inefficient in the central business district because they must stop frequently for cross traffic. PRT networks can be designed so that the vehicles can maneuver to merge and diverge with little loss of average speed, and hence can offer average speeds well in excess of that possible with automobiles. With higher average speeds proportionately fewer vehicles are needed to move a given number of people. Moreover, a properly designed PRT system uses a tiny fraction of the land needed by the automobile system.
The use of very small vehicles running on small-cross-section guideways is not only not an incompatible combination, it, with off-line stations, is the basic combination that make PRT the logical next step in urban public transportation. PRT would not handle all of the traffic in a city as dense as New York, but numerous studies have shown that in most cities, designed correctly, it will have adequate capacity and can attract far more traffic than conventional transit and with superior economics - including control-system costs.
Visual impact of elevated guideway is a problem that requires careful attention, but we have found numerous cases in which small, elevated guideways are enthusiastically accepted once people understand the service, social, and environmental advantages of PRT. The problem of providing empty vehicles has been simulated many times and they are included in all of our economic studies. Properly designed, the average rush-period waiting times are generally less than one minute.
Vuchic claims that all of the people who have worked on PRT have neglected its "fundamental infeasibility." On the contrary, in studying a new system like PRT, the serious investigators have had to study carefully every conceivable problem the system may have. In particular, I have studied and debated with colleagues and antagonists every objection to PRT, including those presented in papers by Professor Vuchic, and find none of substance. Among those willing to be briefed in detail and to have all of their questions and concerns answered, I find great enthusiasm to see the system built.
Vuchic disparages the Chicago Regional Transportation Authority, not, I am quite sure, having any real understanding of the comprehensive questioning and investigation they and Raytheon Company conducted before committing to a $40M program of PRT development. A suburb ( Rosemont ) is a fine location for a first demonstration of a PRT system. It needs to be built and to be shown to work successfully in a less demanding application before being placed in a downtown setting. It is important in any new development program not to take on too much too soon.
Vuchic argues that in a heavily used application, an AGT system would be much more efficient and less costly. In a study at SeaTac International Airport several years ago, this question was asked. It was found that even after quadrupling the estimated cost of a PRT system, it was found to be less expensive per passenger-mile than the best AGT system that could be offered. The PRT system would have many more stations and hence much more accessibility, and would cut the waiting times and trip times substantially. It was unanimously selected by a comprehensive review board.
PRT is not suitable everywhere, but it is suitable in a very wide range of applications and deserves to be demonstrated. While the Morgantown AGT system is not true PRT, it has shown for two decades that it is practical to operate completely automated vehicles in regular daily service. Significant advances in technology since the Morgantown system was designed make the true PRT concept fully practical.
J. Edward Anderson was President and CEO of the TAXI 2000 Corporation. He can be contacted via e-mail at firstname.lastname@example.org
This response has been printed in the Urban Transportation Monitor of December 22, 1996. It is posted here with UTM's permission. Persons interested in contributing written items on this topic for possible publication in the UTM should contact the publisher, Dan Rathbone. He can be reached via e-mail at: email@example.com
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Last modified: October 21, 2008