Automated Guideway Transit

Evolution of AGT

AGT was originally conceived as a means of providing mass transit services to accommodate rider loads exceeding those that could be served by existing buses or trams. While buses and trams offered an easy public transit solution for cities and suburbs suffering from traffic congestion, they did not have sufficient capacity or speed—due to frequent stops along a route—to make them an attractive alternative to transport by one's personal vehicle. While offering greater capacity and speed, subway systems generally were too costly to install in smaller cities and outlying areas. AGT offered a solution to bridge the transit gaps.

In traditional subway systems, the bulk of the cost is due to a need for large vehicle size and correspondingly large tunnels, rails, stations, and common system infrastructure. Part of the reason why large vehicle size is needed is the importance [Page 166]of headway, which is the safety distance required between vehicles traveling with limited sightlines through tunnels. Large vehicles under such conditions require a significant headway distance. Automated transit offered an opportunity to reduce headway requirements greatly and thus the size of vehicles and the necessary supporting infrastructure. With AGT, everything from track supports to station size could be reduced.

Smaller vehicles were lighter as well, which opened the door to a variety of suspension methods, from traditional steel wheels to rubber tires, air cushioning, and magnetic levitation. Automated steering systems still had to contend with issues of turning and rights of way without a person at the helm. For smaller systems, the simplest solution was to use a rigid guideway, such as a single light rail embedded in the ground or wall with an attached wheel pressed against it to steer—or guide—the unmanned vehicle along its set path. Some modern systems have eliminated the rail altogether, replacing it with a virtual one that is read by sensors on the vehicle without the need to have an actual rail or mechanical connection.

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