Guided Bus - Rubber-tyred "trams"

Rubber-tyred "trams"

A further development of the guided bus is the "tramway on tyres", in which a rubber-tyred vehicle is guided by a fixed rail in the ground and draws current from overhead electric wires like a conventional tram. Two incompatible systems exist, the Guided Light Transit (GLT) designed by Bombardier Transportation, and the Translohr system. There are no guide bars on the sides but there is a central guidance rail that, in the case of Translohr, is a special rail that is grasped by a pair of metal guide wheels set at 45° to the road and at 90° to each other. In the Bombardier system, a single double-flanged wheel between the rubber tyres follows the guidance rail. In both cases, the weight of the vehicle is borne by rubber tyres on bogies to which the guide wheels are attached. Power is supplied by overhead lines or by rechargeable batteries in areas where there are no overhead wires.

The Bombardier system has been adopted in Nancy and Caen, France, while the Translohr system is in use in Clermont-Ferrand, France and Tianjin and Shanghai, China, and is under construction in Padua, L'Aquila, and the mainland Mestre district of Venice in Italy. The Translohr system is intended for guidance-only operation, while with the Bombardier system the vehicles can be driven as normal buses as requirements dictate, such as journeys to the depot. The Bombardier vehicles are legally considered buses, and must bear bus-like rear-view mirrors, lights and number plates. Unlike trams, GLT vehicles have a steering wheel, though it is not used when following the guidance rail. Because the Translohr "tram" cannot move without guidance it will probably not be classified as a bus. Hence the Translohr vehicles on test runs on the Clermont-Ferrand network are not equipped with license plates.

These systems offer a much more tram-like experience than a regular guided bus, and offer some advantages over trams, such as a potentially smaller turning radius, the ability to climb steeper gradients (up to 13%), and quieter running around corners. The infrastructure installation can be less complicated than the installation of a complete tram line in an existing street. These systems have been likened to the tram equivalent of rubber-tyred metros, and they are also correspondingly less efficient than steel-wheeled light rail vehicles. There is no evidence to prove the superiority of either guidance system. Both Bombardier Guided Light Transit and Translohr have encountered derailment during operation.

Other experimental bus systems have non-mechanical guidance systems, such as sensors or magnets buried in the roadway. In 2004, Stagecoach Group signed a deal with Siemens AG to develop an optical guidance system for use in the UK.

A further increase in capacity from rubber-tyred trams is rubber-tyred metro. Such systems are in operation in a number of cities, notably some of the lines of the Paris Métro: the system originated in France.