Personal Rapid Transit and Fire Safety

The current discussion item is the first in a series comparing the fire hazards of PRT with those of large vehicle systems.

Fire safety is sometimes cited as a stumbling block to the implementation of a public, small vehicle, automated transit system. Fire is a concern in any vehicle or enclosed space, and PRT systems are no exception. The idea of travelling in an enclosed, elevated, and automated system when a fire breaks out is frightening indeed, but there are several reasons a PRT system will actually be inherently safer than it's large-vehicle cousins. To evaluate the safety risks we will compare the PRT system to the commonly used, large-vehicle transit system with regards to exposure, escape, and response.

The key fire hazards in an electrically powered transit system are the electrical components. Assuming both systems are manufactured and maintained to the same standards, the smaller PRT vehicle exposes the individual to fewer fire risks than a large-vehicle system does. For instance, a large vehicle may require 4 sets of doors with motors, wiring, etc. The PRT vehicle has only two - or even a single door in some designs. A long rail car requires much more wiring than a nine-foot long PRT vehicle, with an increased risk of shorts and failures with each additional foot of wiring.

The drive systems for both vehicle types are usually placed beneath the fire-resistant flooring of the vehicle. In the ACPRT reference system, major electrical components are further isolated from the passenger compartment by being placed on the bogie within the semi-enclosed running space below the chassis. This places an air-gap between any fire in the bogie, limits direct exposure to only the six-inch wide slot in the top of the guideway, and contains the sides of the fire to help prevent flames or smoke from 'wrapping around' the side of the vehicle and gaining access to the less fire-resistant sides of the vehicle, or blocking the exit doors.

The non-stop PRT system also operates at a higher average speed than systems with large vehicles stopping at each station, resulting in less time required for trips of the same length. So the PRT rider is confined to the vehicle for a shorter time and thus spends less time exposed to the electrical components within the vehicle.

A second key fire hazard is people. Through carelessness, negligence, criminal activity, or mental instability, people start fires on transit systems. While no transit system can protect an individual from the risk that they themselves will start a fire, the small, private, PRT vehicle removes exposure to fires other people may start.

Furthermore, most train systems are operated in double or triple car sets much of the time, so riders are also exposed to hazards from the other cars in a train as well as the one in which they are riding. Smoke, for instance, generated by a fire in one vehicle may cause a hazard in the following vehicle. Fire may spread from one vehicle to another in the train. The PRT system maintains a distance between each vehicle of at least 25 feet, limiting the ability of smoke and fire spreading from vehicle to vehicle. Large-vehicle systems are also typically designed with two-way guideways instead of the one-way guideways in a PRT system. Passengers are exposed to smoke and fire risks from passing vehicles as well.

Passenger within the vehicles are not the only ones who may be exposed to fire hazards originating from the system. Those waiting at stations are also at risk. In this regard, PRT's focus on building stations and designing service to reduce or eliminate waiting at stations means far fewer people exposed to a burning vehicle. By design, large-vehicle systems may cause the formation of large crowds waiting for the next train or bus, and those crowded conditions expose many people to any fire incident that may occur.