Critique of Initial Article on PRT by Vukan Vuchic
by Dennis Manning
The Vuchic article on PRT contains some very faulty arguments. The first paragraph begins with the notion that the PRT idea having been around for 30 years makes it an unworthy concept. History is rife with concepts sitting on the shelf for long periods before implementation. The gestation period for the automobile was about 135 years, i.e. from the time the first self-propelled, driver guided (no rail) vehicle was built; it was 135 years before the first Model-T rolled off the assembly line.
Mr. Vuchic argues that only large vehicles are efficient enough to justify the system expense. It would be helpful if he could speak to what kind of efficiency he is talking about. One would think that the predominance of the auto over transit for the past 75+/- years would be a convincing enough argument for the validity of the "single occupant" vehicle. In the simplest terms it is what people prefer.
Virtually every aspect of PRT is more economical than conventional transit, especially when the measure of "efficiency" is the perceived value and convenience of the passenger(s) relative to the cost. Begin with the heart of the system - automatic control. Recent studies of French systems show that even with large vehicle systems automation improves the economics. One of the primary reasons is that vehicles can be deployed to when and where the demand is located. Scheduling is improved. Vehicle dispatch is not dependent on driver work rules. Labor savings are obvious. Safety is better also.
Automation improves the economics for large vehicle systems. PRT can take even more advantage of automation. As vehicles become smaller there is no increase in cost for drivers. It is the increase in the cost of drivers that has conventional transit trapped in large vehicles. The fact that PRT systems will require moving empty vehicles at first seems like a waste. A closer look shows that it is actually the most efficient way to bring passenger and vehicle together. There are basically four ways to bring passenger and vehicle together. The auto system - where extensive parking and sprawl is required, along with huge numbers of vehicles; the transit system - where scheduled vehicles run on line and pay the price in low load factors and long walking distances; the airplane system where passengers are assembled in large batches and have lengthy boarding waits; or the PRT system which has the best balance between parking, load factor, walking distances, and waiting times. Taxi systems are a good example of how this works. Sometimes they cruise, sometimes they park. PRT does a similar balancing act, except one doesn't have to pay dispatchers or idle drivers.
Because of their convenience taxis command far higher fares than transit, further indication of the value of increased LOS and individual use. Then add the higher point to point speed for PRT, even faster than the taxi. The long and short of it is that for less money than conventional transit PRT delivers greatly increased coverage and a far higher LOS.
Taxis highlight another questionable proposition by Mr. Vuchic. In speaking about the Morgantown AGT (Automated Group Transit) he argues that one AGT vehicle carrying fifteen passengers is more efficient than 10-12 PRT vehicles, if fifteen persons want to travel. It is the "if fifteen persons want to travel" statement that is erroneous. That is seldom the case. More likely is that any collection of 15 people will want to go fifteen different places. If the 15 passenger vehicle is the most efficient, why are taxis not predominately van size? Van size vehicles are used in specialized situations, but they are not as pervasive as taxis for typical urban areas. And is there a shorter wait time for vans rather than taxis? As he claim would be the case for one AGT versus more numerous PRTs. Just the opposite is true.
Examine his statement "If the PRT attracts few customers, it would represent an expensive version of the private car. Is that what is needed, when the main cause of our congestion and waste in transportation is caused by our excessive reliance on private vehicles with low occupancy?" Of course that isn't what is needed and at any rate the low use expensive PRT system he postulates would defeat itself. The question is nonsensical. It would have no bearing on existing transportation. If on the other hand he is suggesting that such a system could become widespread because a few people were willing pay a very high price for PRT, he shoots down all his arguments about capacity problems. I believe the statement reveals a fixation on low occupancy vehicles as being the problem. For lo these many years mass transit advocates have railed against the low occupancy vehicle while the world goes the other way. There is NOTHING in the mass transit approach to suggest any change in the congestion and waste that he cites. PRT by its very nature takes the congestion out of the trip. As for possible congestion/capacity problems at the PRT station:
The congestion/capacity issue - a very flawed argument by Mr. Vuchic when he claims PRT cannot adequately meet demand. PRT stations have the flexibility to be sized to demand. Moving empty vehicles further enhances the ability to handle peak loads, and stations can be dispersed to avoid the concentrations of conventional transit. Multiple berth stations can be built to cover the problem of one vehicle waiting for others. More to the point, PRT that has demand volumes that approach system capacity in all likelihood can be operated profitably. Mr. Vuchic cannot have it both ways, either PRT will have enough demand to be successful or it will not.
The argument of not being environmentally acceptable - compared to what? PRT is much smaller and lighter than conventional transit resulting in less visual and noise pollution. At grade transit pays an environmental price in increased congestion and lower safety. Elevated structures are the trade off for conflicts with existing systems whether you are talking transit or PRT. PRT also has distinct environmental advantages in lower disruption during construction. The recent problems in building the Los Angeles transit system come to mind.
No place to implement PRT?? The Raytheon Corporation has identified over 30 sites for future PRT systems. PRT has enormous potential in allowing land use patterns to take advantage of the new paradigm. An example was recently presented at the International PRT Conference in Minneapolis . It clearly showed how an entire airport complex could be designed around PRT at tremendous savings in space, environment, efficiency, and safety. It probably would be opposed by the hundreds of employees drawing salaries to move people and baggage at existing airports. It would, however, be a tremendous boon to employment in surrounding businesses and services. Non-stop from hotel to boarding area! Skip the long concourses and wrestling with baggage!
That leads to two more points. (1)Driverless vehicles offer cargo moving potential that is virtually non existent with conventional transit, and (2) the fact that PRT has been rejected by many existing transit authorities. Rejection by authorities is a weak argument about PRT merits. Existing authorities have a long record of failing to see the potential in a new technology. Railroads panned the upstart automobile. They not only missed the auto they didn't see the trucks either. Steamship companies didn't see the airplane coming, and so on.
With the long decline in market share for transit both in the US and globally, whatever so called efficiency exists in transit systems is a rather moot point. However, we do agree on one point. The experience (successful or unsuccessful) of the Raytheon Rosemont project should go a long way towards clarifying the picture. In the final analysis we can speculate endlessly about how PRT will or will not perform. The only way to really know is to put one or more into real world situations. Compared with the money devoted to mass transit projects that our seventy plus years of experience tells us are doomed to failure even before they are built, a PRT experiment or two is a quite reasonable proposition.
In the final analysis what Mr. Vuchic does is over estimate the cost of PRT while under estimating its flexibility and the value of the convenience and service it offers.
One last note. It is ironic that the transit systems, which have the advantage of total control, and therefore a leg up on the auto/highway system, are way behind the highway people who are spending heavily on their AHS approach. The highway people apparently recognize the value in automated individual use vehicles where the transit people do not. In this writers opinion, in the end, the AHS people will come to the conclusion that it is better to build a separate dedicated guideway (only a hairs breath away from PRT concept) than to go through the lengthy, vastly expensive and tortuous evolution of the existing system, but that is another subject.
Dennis Manning was an Associate Transportation Planner with Caltrans, currently retired. These opinions are his alone and do not reflect any Caltrans positions on this topic.
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Last modified: 21 October 2008