Rubber-tired metro is an intermediate form between rail and road transport: the vehicles have wheels with rubber tires 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 tire. As on a railway, the driver does not have to steer (which would be very difficult on such a 'road'), because the vehicle has additional horizontal guiding wheels, also with rubber tires, 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 tire and at switcheses. In Paris, while converting metro lines from conventional rail to rubber-tire technology, these rails were also used to enable mixed traffic with rubber-tired and steel-wheeled trains using the same track. Other systems (e.g., Lille) have other sorts of flat tire 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-tired 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. This ability to deal with slopes can improve energy efficiency because the tunnel can be built in a basin-shaped profile between stations, allowing the trains to use the downslope to accelerate from rest and the upslope to decelerate, as is the case in Montreal. The use of this method is not unique to rubber-tired systems; in fact, it was pioneered on London Underground's Central Line with conventional rail technology as early as 1900.
However, there are strong disadvantages to rubber-tired systems, as well. Rubber tires have considerably more friction, than the optimal combination of steel wheel on rail. This leads to more energy consumption. And, it is an unnecessarily 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.
Also, the quality of ride is mediocre at best, with a choppy quality to it. Noise levels are also not appreciably lower than most traditional steel rail metro systems and much higher than some high quality systems, such as the U-Bahn system in Munich, Vienna and Berlin.
Rubber-tired metro was first applied to the Paris Metro, developed by Michelin (who provided the tires 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-tired metro is applied to new systems or lines only, including (new) line 14 Madeleine-TGB in Paris.
It is also important to understand how the rubber-tired technology came about to begin with. 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 and compensate for the years of neglect suffered during the occupation.
At the same time, De Gaulle sought to differentiate the French and their way of doing things, as well as create a morale booster. De Gaulle posed the question as to how that might be applied to the Paris Metro rebuilding and the rubber-tired technology became one of the manifestations of the French "coming back". So, for the most part, the real impetus for implementing this burdensome system was political, not technical merit. Nevertheless, the French have succeeded in propagating and exporting this technology, as "state-of-the-art" and au courant.
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-tired metro system was built in Montreal, Canada; see Montreal metro. A few more recent rubber-tired 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. Some automated driverless systems have since been built using conventional rail technology, such as London's Docklands Light Railway.
Here are some cities that have at least partly rubber-tired metro systems:
tram connects central Tokyo, Japan with the Tokyo harbour area.