Automated guideway transit

AGT covers a wide variety of systems, from limited people mover systems commonly found at airports, to more complex automated train systems like the Vancouver SkyTrain. In the people mover role the term "automated people mover" (APM) is sometimes used, although this distinction is relatively rare because most people movers are automated. Larger systems span a variety of conceptual designs, from subway-like advanced rapid transit (ART) systems to smaller (typically two to six passengers) vehicles known as personal rapid transit (PRT) which offer direct point-to-point travel along a switched network.

Origins in mass transit

AGT was originally developed as a means of providing mass transit services aimed at serving rider loads higher than those that could be served by buses or trams, but smaller than those served by conventional subways. Subways were too expensive to build in areas of lower density, such as smaller cities or the suburbs of larger ones, which often suffer the same gridlock problems as larger cities. Buses could be easily introduced in these areas, but did not offer the capacities or speeds that made them an attractive alternative to car ownership. Cars drive directly from origin to destination, while buses generally work on a hub-and-spoke model that can increase trip times.

AGT offered a solution that fit between these extremes. Much of the cost of a subway system is due to the large vehicle sizes, which demand large tunnels, large stations and considerable infrastructure throughout the system. The large vehicles are a side-effect of the need to have considerable space between the vehicles, known as "headway", for safety reasons due to the limited sightlines in tunnels. Given large headways and limited average speed due to stops, the only way to increase passenger capacity is to increase the size of the vehicle. Capital costs can be reduced by elevating the tracks instead of burying them, but the large tracks needed present a major visual barrier, and the steel-wheels-on-steel-rails are very noisy rounding bends.

Headway can be reduced via automation, a technique that was becoming feasible in the 1960s. As the headway is decreased, the size of vehicle needed to transport a given number of passengers per hour also decreases, which, in turn, decreases the infrastructure needed to support these smaller vehicles. Everything from track supports to station size can be reduced, with similar reductions in capital costs. Additionally, the lighter vehicles allow for a wider variety of suspension methods, from conventional steel wheels, to rubber tires, air cushion vehicles and maglevs. Since the system has to be automated in order to reduce the headways enough to be worthwhile, by automating the steering as well the operational costs can also be reduced compared to crewed vehicles.

One key problem in an automated system is the steering system's negotiation of turns in the right-of-way. The simplest solution is to use a rigid guideway, like conventional rails or steel rollercoasters. For lighter AGTs, these solutions were over-specified given the size of the vehicle, so the guideway was often separate from the running surface. Typical solutions used a single light rail embedded in the ground or attached to the guideway wall, with a wheel or slider that was pressed against the guideway rail and steered the running wheels through a linkage. A suspension-like system is needed to smooth out the imperfections in the guideway and provide a comfortable ride. More modern systems can eliminate the rail and replace it with a "virtual" one that is read by sensors on the vehicle without the need for any mechanical connection.

AGT systems, and the personal rapid transit concept (or "dial-a-cab"), became a major area of research after the publication of the HUD reports in 1968, and subsequent funding by the US Department of Transportation. Political support was particularity strong in states with large concentrations of aerospace companies; with the ending of Project Apollo and the winding down of the Vietnam War, there was concern that these companies would be left with few projects in the 1970s and 80s. Expecting widespread deployment of PRT systems through the late 1970s and 80s, many of the major US aerospace companies entered the AGT market, including Boeing, LTV and Rohr. Car companies followed suit, including General Motors and Ford. This, in turn, sparked off a wave of similar developments around the world.

However, the market for these systems proved to be overestimated, and only one of these US-designed small AGT's was constructed as a mass transit system, the Morgantown PRT.