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On a strictly economic basis, one-person vehicles minimize capital cost, but they do not serve obvious social needs. Two-person vehicles are too small for a small family, for taking luggage, or for a wheelchair plus attendant. Also, if a party of three wants to travel together, one of them would have to ride alone if the vehicles hold only two persons, which may be socially awkward. So the vehicle should have room for at least three seats side-by side. If the vehicle were to have to accommodate a wheelchair which can rotate to face forward, the floor area is such that there can be two forward-facing seats in the back and two backward-facing seats in the front, which could normally fold up to accommodate the wheelchair. This provides a socially pleasant configuration for occasional use by two couples, but requires the vehicle to be longer, which increases vehicle weight and cost, and station length and cost. (An alternative is to provide special vehicles for wheelchairs, which would be on call by cellular telephone on short notice.)  | | Interior of 3-Passenger Cab | From the viewpoint of ultimate safety, a passenger can be protected in a sudden stop if he or she is behind a padded dashboard. The above four-passenger configuration has a much longer throw distance than a side-by-side seating configuration and therefore greater probability of injury in the unlikely event of a sudden stop. Since each vehicle will be controlled by a pair of checked-redundant fault-tolerant computers, the probability of a sudden stop will be low, yet such a stop must be considered in the design. Since more than 95 percent of the trips in an urban area are taken by one, two or three persons travelling together, the more people an individual vehicle is required to accommodate, the more vehicle dead weight there is per person carried and higher capital and energy cost. By charging a fare per vehicle rather than per person, it is possible that the average vehicle occupancy can be increased over that experienced with automobiles. We see that the factors that must be considered in picking vehicle capacity are not the same in PRT as in a family automobile. A PRT trip is generally quite short and a group larger than can fit into one vehicle can take two or more vehicles, which leave the origin station seconds apart and arrive at the destination seconds apart. Taxi 2000 is designed to carry a total load of 650 lbs.
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