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Won't a system of many small vehicles cost more than a system of a few large vehicles? |
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Written by Administrator
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Friday, 09 February 2007 |
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The basic features of PRT follow logically as features that minimize the total cost per passenger-mile. These features permit true minimization of guideway cost, vehicle-fleet cost, and operating cost while maximizing service.  | | Vehicle Cost per Unit Capacity | -
Data shows that transit vehicles cost about the same per unit of capacity no matter how large or small they are. Contrary to intuition, there is no economy of scale. By using nonstop trips, possible with off-line stations, the average trip time of a PRT system is two to three times less than in a conventional transit system, which means that the fleet capacity (number of vehicles x capacity per vehicle) and therefore fleet cost needed to serve a given number of trips is less by the same factor. -
Vehicles of the size required to hold up to three or four seated adults have a much smaller cross section and weigh substantially less per unit of length than large standing-passenger vehicles, and, because of much lower dynamic loading, lead to lower guideway weight (15 times lower) and lower cost. -
To compare operating and maintenance (O&M) costs, we define a quantity called a "place-mile." The number of place-miles of travel in a transit system consisting of vehicles or trains of any size is the number of vehicle-miles of travel multiplied by vehicle capacity. A vehicle-mile is one vehicle traveling one mile. Because PRT vehicles move only when service is demanded, the total number of place-miles per day required to serve a given level of passenger demand is only about a third as much as in a conventional scheduled transit system. Examination of data on O&M costs shows that the O&M cost per place-mile is nearly the same regardless of the type of transit system. Thus the O&M cost of a transit system that carries a given number of people per day is proportional to the number of place-miles per day of travel.
The remarkable result of this kind of systems-economic analysis is a transit system in which the features required to minimize both capital and operating costs are exactly those that provide maximum service, i. e., on-demand, alone or with one or two friends, in seated comfort, any time of day or night, at a predictable average speed two to three times that possible with conventional transit. The only reason for using large vehicles in urban transportation is to amortize the wages of drivers over as many fare-paying riders as possible. Automation permits relaxation of system characteristics toward a true optimum.
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