Rubber-tyred metro

A rubber-tyred metro (or rubber-tired in non-British English) 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 inside a guideway for traction, as well as traditional railway steel wheels with flanges on steel tracks for guidance. 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. See also Rubber-tyred trams and Bombardier Guided Light Transit.

History

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 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; see Montreal Metro. 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 the first automated rubber-tyred system opened in Kobe (Japan) in February 1981. It is the Portliner linking Sanomiya railway station with Port Island.

Technology

Overview

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 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 rollways, each the width of a tyre are used, either of concrete (Montreal Metro, Lille Metro, Toulouse Metro, most part of Santiago Metro), 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. [cite web
url=http://www.urbanrail.net/as/sapp/sapporo.htm
title=UrbanRail.Net > Asia > Japan > Sapporo Subway (Metro)
publisher=www.urbanrail.net
accessdate=2008-04-15] The VAL system used in Lille and Toulouse has conventional track between the guide bars.

On some systems (e.g., Paris, Montreal, 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 difference between rubber-on-concrete and steel-on-steel is that rubber-on-concrete generates more friction. This results in various pros and cons.

Advantages

Advantages of rubber-tyred metro systems (compared to steel wheel on steel rail):
* Smooth ride (with little "jostling" around)
* Faster accelerationref|a1
* 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.
* Quiet ride in open air (for residents and those outside the train)

# Modern steel-on-steel rolling stock using distributed-traction with a high-proportion of powered axles, have narrowed the gap to the acceleration/performance found in rubber-tyre rolling stock.

Disadvantages

The higher friction causes disadvantages (compared to steel wheel on steel rail):
* Higher energy consumption than steel-on-steel
* A larger quantity of excess heat is generated
* Weather variance. Losing the traction-advantage in inclement weather (snow and ice)ref|b1
* Heavier; steel rails remain for switching purposes, and as a safety backupref|b2
* Tyre replacement costref|b3
# To reduce weather disruption, the Montreal Metro runs 100% underground. On Paris Métro Line 6, upgrades of tyres (as used with cars) and special ribbed tracks have been trialled.
# In effect, there are two systems running in parallel. This is more expensive to build, install and maintain.
# Rubber tyres have higher wear rates and therefore need more frequent replacement. Although a steel wheels set is more expensive than a pair of tyres, the frequency of their respective replacements makes rubber tyres the more expensive option. And in addition many rubber tyres for guidance will be needed, too.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.

imilar technologies

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, 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

ee also

* VAL (Véhicule Automatique Léger)

References

* Bindi, A. & Lefeuvre, D. (1990). " _fr. Le Métro de Paris: Histoire d'hier à demain," Rennes: Ouest-France. ISBN 2-7373-0204-8. fr icon
* Gaillard, M. (1991). " _fr. Du Madeleine-Bastille à Météor: Histoire des transports Parisiens," Amiens: Martelle. ISBN 2-87890-013-8. fr icon
* [http://www.emdx.org/rail/metro/principeE.html Marc Dufour's "The principle behind the rubber-tired metro".] en icon

External links

* [http://www.infovisual.info/05/050_en.html TRUCK (bogie)]