Transit Technology: Fundamentals and Subsequent Development

This is a series of articles by Sky Train Corporation, discussing the foundation and development of some familiar details of transit technology. The text reflects to some extent the separate functions that the different transit components can serve, a way  of  slotting the ideas into compartments. For example, the size and design of vehicle bodies depends upon the load-carrying capacity of the trucks and track, the size of body that the clearances and curves of the right of way can accept, and on the nature of the traffic to be carried, such as short-haul commuter traffic, inter-city passengers, airport feeders, and the various types of freight traffic. Given these constraints, the nature of body design follows basic principles.

Article #3: Heavy rail transit, light rail transit (LRT), and monorails

Commuter rail operates along general user railroad tracks, often mixed with industrial switchers, freight and long haul passenger trains. This mix requires that the cars shall be of strength to meet the AAR requirements, of 800,000lbs compressive strength at the couplers. The tracks may make crossings at grade with highways and city streets. Cars can be large, of the size usually associated with long haul trains, 3.0m (10ft) wide, and up to 25.5m (85ft) long. These cars may be provided with a good proportion of seating, with adequate standing space for passenger circulation. Double deck cars can carry up to 300 passengers each, or 3,000 passengers on a train of ten cars. Propulsion may be by locomotive, diesel or electric, or by multiple unit cars, also diesel or electric, if the rail line is so equipped. Trains can be long, ten cars or more, and the distance between stations may be relatively long, from 2km up to 7 or  8 km. For such services, power on the train achieves high railroad speeds between stations, from 100km/h up to 150km/h. Acceleration is not necessarily high, so that hauling by locomotive is acceptable. In North America, station platforms are usually at ground level, so that passengers must ascend and descend the car steps. Many other countries provide station platforms at car floor height, allowing a level walk-in for passengers, affording shorter dwell times.

Heavy rail subway operations: subways generally operate in tunnels under the city streets, but may pass to the surface in the outer suburbs. For this reason, propulsion is essentially electric, either by third rail or overhead catenary. The tunnels are likely to accept cars of the same width as the commuter rail, that is 3.0m (10ft), but the lengths of the cars may be limited because of sharp curvature in the tunnel alignment.. Many subway cars are about 15m (50ft) long, with a few seats, but mostly standing space. Passengers will spend relatively short time in transit, and high standing capacity is more important than seats. It is unusual for heavy subway to make grade crossings with streets, being fully grade separated all the way.

In subways designed for trains on rubber tires, cars are lighter and narrower, from 2.4m (8ft) to 2.6m (8ft8ins). Such services still would be designated as heavy rail subways.

Light rail transit (LRT): is derived from earlier street car practice. Cars may be narrow enough to be accepted on the street, as narrow as 2.25m (7ft 6ins) to 2.4m (8ft), running as a mix with other street traffic, and as short as 12.0m (40ft), to be able to pass round street corners. In any case, these cars are much smaller and lighter than railroad cars. The original intent has been to continue street operations where necessary, but recently more value has been placed on the merits of exclusive right of way, so that planners look for possible alignments that would allow separation from other street traffic. In some cases, tracks laid in the streets have been isolated with curbs, so that automobiles cannot interfere with the LRT movements. This absorbs existing roadway capacity. Cars are operated in short trains, with an operator on each train, and the frequency is matched to the demands of inner city passenger travel. Peak service can be as frequent as at two minute headway, with off-peak service at four to six trains per hour.

Monorail: the mechanical arrangement of monorails covers a wide rage of possibilities. Most monorail concepts have the objective of creating a light-weight, low cost system, implying also a limited carrying capacity. The beams are as light as possible, spans between columns to match, cars are small and the operation is low speed. For these reasons, applications have been for special uses, as in theme parks or tourist centers. A few operating monorails exist, and are well proven in practice. Many more concepts have been advanced, that are now at the promotional stage. The main differences are whether the vehicles ride on trucks on top of the rail, which then takes the form of a monobeam, or are suspended below the beam, in which case the body may be suspended beneath trucks that ride on the outside of a monobeam, or that ride inside a duct, making it a monoduct.

Bottom supported monobeams: the first monobeams were developed in Germany, on the Alweg system. This has been subject to later development. Examples of such systems have been in operation for several years in Disney theme parks, in Sydney, Australia, and one was used for access to the World’s Fair in Seattle, WA. A precast concrete beam, up to 1.0m wide and some 1.0 to 2.0m deep, is supported from below on columns, spaced at appropriate intervals. The vehicles ride on top of the rail. In most cases, the vehicles are narrow, running on rubber tires, that do not have a self-steering capability, so the cars have skirts down each side of the beam, with lateral wheels to guide them, and lower wheels to hold the cars in an upright position. Electric contact strips are attached to the sides of the beam to transmit power to the cars, and to activate signal and control systems for train separation.

Suspended monoducts: An operating example of the “H-Bahn” by Siemens exists on the campus of the university in Dortmund, Germany. The duct has ledges on the inside, carrying roadway surfaces for rubber tires to ride on. The vehicles are small, and are suspended beneath trucks on these wheels. There are horizontal wheels for guidance and steering, bearing against the inner walls of the duct. The carrying capacity of this system is limited, and no widespread market has developed.

A true monorail, suspended beneath a single steel rail, has been in continuous operation in Wuppertal, Germany for almost 100 years, serving the same purpose as a city street car, and currently transports up to 70,000 passengers per day. The track passes along city streets and along the River Wupper, with stations spaced at approximately 1.0km intervals. The cars have two bodies, articulated, and operated by a motorman under an automatic block signal system.