Rubber-tyred metro is an intermediate form between rail and road transport: the vehicles have wheels with rubber tyres like a bus, but using a set of two parallel concrete (e.g., Lille, Toulouse) or corrugated steel (e.g., Paris) rollways, each with the width of a tyre. As on a railway, the driver does not have to steer, because the vehicle has horizontal guiding wheels, also with rubber tyres, rolling along guide bars on both sides of the track.
On some systems (e.g., Paris), between the rollways there is a regular railway track, and the vehicles additionally have classic metal rail wheels, but these are normally at some distance above the rails and hence not used; they take over in the case of a flat tyre and at switches. In Paris, while converting metro lines from conventional rail to rubber-tyre technology, these rails were also used to enable mixed traffic with rubber-tyred and steel-wheeled trains using the same track. Other systems (e.g., Lille) have other sorts of flat tyre compensation and switching methods.
The vehicle is electric, with power supplied by one of the guide bars, which thus also serves as the third rail (the current is not picked up through the horizontal wheels, but through a separate lateral pickup shoe). The return current passes through a return shoe to one of the rails, or to another guidebar depending on the type of system.
The advantages of rubber-tyred metro systems include quietness of operation, faster acceleration, shorter braking distances, and ability to climb or descend steeper slopes than would be feasible with conventional rail technology.
However, there are strong disadvantages to rubber-tyred systems, as well. Rubber tyres have considerably more friction, than the optimal combination of steel wheel on rail. This leads to more energy consumption. And, it is a more complex technology, using proprietary components, sharing little standardization with steel wheel systems. Weight advantages are minimal, because the traditional steel wheels and rails are still a part of the system as a safety backup. So, in effect, there are two systems running in parallel. This is expensive to build, install and maintain.
The quality of ride can be variable. Noise levels are also not appreciably lower than most traditional steel rail metro systems and can be higher than some.
Rubber-tyred metro was first applied to the Paris Metro, developed by Michelin (who provided the tyres and guidance system) in collaboration with Renault (who provided the vehicles). Starting in 1951, an experimental vehicle operated on a test track between Porte des Lilas and Pré Saint Gervais, a section of line not open to the public. Line 11 Châtelet-Mairie des Lilas was the first line open to the public converted in 1956, chosen because of its steep grades. This was followed by line 1 Château de Vincennes-La Défense in 1964 and line 4 Porte d'Orléans-Porte de Clignancourt in 1967, converted because they had the heaviest traffic load of all Paris Metro lines. Finally, line 6 Etoile-Nation was converted in 1974 to cut down noise pollution on its many elevated sections. Because of the high cost of converting existing rail-based lines, this is no longer done in Paris, nor elsewhere; now rubber-tyred metro is applied to new systems or lines only, including (new) line 14 Madeleine-TGB in Paris.
During the World War II German occupation of Paris, the Metro system was used to capacity, with relatively little maintenance performed. At the end of the war, the system was so worn out that thought was given as to how to renovate the system. At the same time, Charles de Gaulle sought to differentiate the French and their way of doing things, as well as create a morale booster. So the real impetus for implementing this burdensome system was political, not technical merit. Nevertheless, the French have succeeded in propagating and exporting this technology.
Though these systems have a certain novelty and panache to them, they have not been widely adopted, except by the few cities listed below.
The first completely rubber-tyred metro system was built in Montreal, Canada; see Montreal metro. A few more recent rubber-tyred systems have used automated, driverless trains; the first such system, developed by Matra, opened in 1983 in Lille, and another has since been built in Toulouse. (Automated driverless systems are not exclusively rubber-tyred; many have since been built using conventional rail technology, such as London's Docklands Light Railway and Vancouver's SkyTrain.) Most monorail manufacturers also prefer rubber tyres.
Cities with at least partly rubber-tyred metro systems:
- South Island and West Island lines of MTR - planning
- Bindi, A. & Lefeuvre, D. (1990). Le Métro de Paris: Histoire d'hier à demain, Rennes: Ouest-France. ISBN 2737302048. (French)
- Gaillard, M. (1991). Du Madeleine-Bastille à Météor: Histoire des transports Parisiens, Amiens: Martelle. ISBN 2878900138. (French)