Automated guideway transit

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An automated guideway transit (AGT) or automated fixed-guideway transit

have been implemented. The guideway provides both physical support, like a road, as well as the guidance.

AGT covers a wide variety of systems, from limited

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,

. 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

. 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

. 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

.

Small systems

Dallas/Fort Worth International Airport

Small scaled AGT systems are also known as people movers. Although the mass transit world showed a lack of interest, AGT systems quickly found a number of niche roles that they have continued to fill to this day.

, China.

Over time, the aerospace firms that had initially designed most of these systems left the industry and sold off the AGT divisions to other companies. Most of these were picked up by existing transportation conglomerates, and through additional mergers and buyouts, many of these are today owned by either

systems, provide AGT systems for the airport market.

Large systems

Although the smaller vehicle systems were not successful in the marketplace, larger AGT were simpler to integrate into existing mass transit systems. Many higher capacity AGT systems that looked and operated in a fashion similar to a

, are becoming more common AGT systems. Monorails are less obtrusive because they only require a single, narrow guidebeam.

AGT renaissance

Once limited to larger airports and a small number of metro systems, AGT have undergone something of a renaissance since the late 1990s. Lower capital costs compared to conventional metros have allowed AGT systems to expand quickly, and many of these "small" systems now rival their larger counterparts in any measure. For instance, the

which pre-dates it by 30 years.

Although the original introduction of PRT systems did not result in the widespread adoption as expected,

ULTra

, to connect Terminal 5 with the long-term carpark; its full operation began in September 2011.

See also

References