A rubber-tyred metro is a form of rapid transit system that uses a mix of road and rail technology. The vehicles have wheels with rubber tyres which run on rolling pads inside guide bars for traction, as well as traditional railway steel wheels with deep flanges on steel tracks for guidance through conventional switches as well as guidance in case a tyre fails. Most rubber-tyred trains are purpose-built and designed for the system on which they operate. Guided buses are sometimes referred to as 'trams on tyres', and compared to rubber-tyred metros.
The first idea for rubber-tyred railway vehicles was the work of Scotsman Robert William Thomson, the original inventor of the pneumatic tyre. In his patent of 1846 he describes his 'Aerial Wheels' as being equally suitable for, "the ground or rail or track on which they run". The patent also included a drawing of such a railway, with the weight carried by pneumatic main wheels running on a flat board track and guidance provided by small horizontal steel wheels running on the sides of a central vertical guide rail.
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 it. Rubber-tyred metro technology was first applied to the Paris Métro, developed by Michelin, who provided the tyres and guidance system, in collaboration with Renault, who provided the vehicles. Starting in 1951, an experimental vehicle, the MP 51, 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 to be converted, in 1956, chosen because of its steep grades. This was followed by Line 1 Château de Vincennes - Pont de Neuilly in 1964, and Line 4 Porte d'Orléans - Porte de Clignancourt in 1967, converted because they had the heaviest traffic load of all Paris Métro lines. Finally, Line 6 Charles de Gaulle - Étoile - Nation was converted in 1974 to cut down train noise 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 metros are used in new systems or lines only, including the new Paris Métro Line 14.
The first completely rubber-tyred metro system was built in Montreal, Canada in 1966; see Montreal Metro. Santiago Metro and Mexico City Metro are based on Paris Métro rubber-tyred trains. A few more recent rubber-tyred systems have used automated, driverless trains; one of the first such systems, developed by Matra, opened in 1983 in Lille, and others have since been built in Toulouse and Rennes. Paris Metro Line 14 was automated from its beginning (1998), and Line 1 was converted to automatic in 2007-2011. The first automated rubber-tyred system opened in Kobe, Japan in February 1981. It is the Portliner linking Sanomiya railway station with Port Island.
The vehicle is in the form of electric multiple unit, with power supplied by one, or both, 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 the top of one, or both of the rails, or to the other guide bar, depending on the type of system.
The type of guideway used on a system varies between networks. Two parallel roll ways, each the width of a tyre, are used, either of concrete (Montreal Metro, Lille Metro, Toulouse Metro, most part of Santiago Metro), concrete slab (Busan Subway Line 4), H-Shape hot rolled steel (Paris Métro, Mexico City Metro, the non-underground section of Santiago Metro), or flat steel (Sapporo Municipal Subway). As on a railway, the driver does not have to steer, because the system relies on a redundant system of railway steel wheels with flanges on steel rail tracks. The Sapporo system is an exception as it uses a central guide rail only. The VAL system used in Lille and Toulouse has conventional track between the guide bars.
On some systems (such as Paris, Montreal, and Mexico City), there is a regular railway track between the rollways and the vehicles also have railway wheels with larger (taller) than normal flanges, but these are normally at some distance above the rails and are used only in the case of a flat tyre and at switches/points and crossings. In Paris these rails were also used to enable mixed traffic with rubber-tyred and steel-wheeled trains using the same track, particularly during conversion from normal railway track. Other systems (e.g. Lille and Toulouse) have other sorts of flat tyre compensation and switching methods.
The essential differences between rubber-on-concrete and steel-on-steel are that rubber-on-concrete generates more friction and higher rolling resistance which results in various pros and cons.
Advantages of rubber-tyred metro systems (compared to steel wheel on steel rail):
- Smoother rides (with little jostling around)
- Faster acceleration
- Shorter braking distances, allowing trains to be signalled closer together
- The ability to climb or descend steeper slopes (~gradient 13%) than would be feasible with conventional rail tracks, which would likely need a rack instead. For example, the rubber-tyred Line 2 of the Lausanne Metro has grades of up to 12%
- Quieter rides in open air (both inside and outside the train)
- Greatly reduced rail wear with resulting reduced maintenance costs.
The higher friction and increased rolling resistance cause disadvantages (compared to steel wheel on steel rail):
- Higher energy consumption
- Possibility of tyre blow-outs - not possible in railway wheels.
- More heat generated.
- Weather variance. (Applicable only to above-ground installations)
- Heavier as steel rails remain for switching purposes, to provide electricity or grounding to the trains and as a safety backup
- Tyre replacement cost; contrary to rails using steel wheels, which can be easily repaired at little cost 
- Create air pollution; tyres break down over time and turn into particulate matter.
- ^ Modern steel-on-steel rolling stock using distributed-traction with a high-proportion of powered axles narrowed the gap to the acceleration/performance found in rubber-tyre rolling stock.
- ^ To reduce weather disruption, the Montreal Metro runs completely underground. On Paris Métro Line 6, upgrades of tyres (as used with cars) and special ribbed tracks have been tried out.
- ^ In effect, there are two systems running in parallel so it is more expensive to build, install and maintain.
- ^ Rubber tyres have higher wear rates and, therefore, need more frequent replacement. Although steel wheels set is more expensive than tyres, the frequency of their respective replacements makes rubber tyres the more expensive option. Rubber tyres for guidance are needed.
Although it is a more complex technology, most rubber-tyred metro systems use quite simple techniques, in contrary to guided buses. Heat dissipation is an issue as eventually all traction energy consumed by the train — except the electric energy regenerated back into the substation during electrodynamic braking — will end up in losses (mostly heat). In frequently operated tunnels (typical metro operation) the extra heat from rubber tyres is a widespread problem, necessitating ventilation of the tunnels.
Automated driverless systems are not exclusively rubber-tyred; many have since been built using conventional rail technology, such as London's Docklands Light Railway, the Copenhagen metro and Vancouver's SkyTrain, the Disneyland Resort Line which uses converted rolling stocks from non-driverless trains, as well as AirTrain JFK which is linking JFK Airport in New York City with local subway and commuter trains. Most monorail manufacturers prefer rubber tyres.
List of systems
|United States||Phoenix, Arizona||PHX Sky Train (2013 Phase 1)||Bombardier's INNOVIA APM 200|
|Republic of Korea||Uijeongbu||Uijeongbu Line (Aug 2011)|
|Suwon||one line, name not yet announced|
|Gwangmyeong||one line, name not yet announced|
|Macau||N/A||Macau Light Transit System|
|Turkey||Istanbul||three lines, name not yet announced|
|Wikimedia Commons has media related to Rubber-tyred metro.|
|Wikimedia Commons has media related to Rubber-tyred rolling stock.|
- GB 10 June 1846 10990
- Tompkins, Eric (1981). "1: Invention". The History of the Pneumatic Tyre. Dunlop Archive Project. pp. 2–4. ISBN 0-903214-14-8.
- "UrbanRail.Net > Asia > Japan > Sapporo Subway (Metro)". www.urbanrail.net. Retrieved 2008-04-15.
- Bindi, A. & Lefeuvre, D. (1990). Le Métro de Paris: Histoire d'hier à demain, Rennes: Ouest-France. ISBN 2-7373-0204-8. (French)
- Gaillard, M. (1991). Du Madeleine-Bastille à Météor: Histoire des transports Parisiens, Amiens: Martelle. ISBN 2-87890-013-8. (French)