Urban rail transit

Urban rail transit is an all-encompassing term for various types of local rail systems serving urban or older suburban areas. The vast majority of modern urban rail vehicles run on electricity. The set of urban rail systems can be roughly subdivided into four categories, which sometimes overlap, causing some systems or lines to have aspects of each.

Urban rail transit types

Trams

Trams are systems that runs mainly or completely along streets, with low capacity and frequent stops. Passengers usually board at street- or curb-level (but low-floor trams and level boarding platforms may be used). These can be called "trams", "streetcars", or "trolleys", while the longer-distance lines which have now mostly vanished were called "interurbans" or "radial railways".

Light Rail

Light rail is a relatively new term, as an outgrowth of trams/streetcars. Speeds are usually higher, and articulated vehicles may be used to increase capacity. Note that some systems called "light rail" have most or all of the characteristics of "rapid transit" (see below) and may be better placed in that category, while others are essentially trams referred to as light rail for political reasons.

Rapid Transit

A rapid transit, underground, subway, tube, elevated, or metro(politan) system is a railway—usually in an urban area—with a high capacity and frequency of service, and grade separation from other traffic. In most parts of the world these systems are known as a "metro", in London, England the system is called the "underground", while in most of North America and in Glasgow, Scotland it is a "subway".

Monorail

Monorail is a metro or railroad with a track consisting of a single rail (actually a beam), as opposed to the traditional track with two parallel rails. Monorail vehicles are wider than the beam they run on.

Variations

Terms typically used for one type of system are sometimes used for the other. For example, Boston's Green Line is referred to as a "subway", despite having street-running portions. The Docklands Light Railway in London is a predominantly-elevated system which provides a metro-style service with more in common with the rapid transit definition above than that of light rail; it is so named to distinguish it from the London Underground, which uses longer trains of heavier vehicles to provide more frequent service.

Many cities use names such as "subway" and "elevated railway" to describe their entire systems, even when they combine both methods of operation. Slightly less than half of the London Underground's tracks, for example, are actually underground; New York City's subway also combines elevated and subterranean stations, while the Chicago El and Vancouver SkyTrain use tunnels to run through central areas.

Other types of services

Passenger rail

Other types of passenger rail include the following:
*"Funiculars" are inclined railways that carry passengers up and down steep slopes.
*"Regional rail" or "commuter rail" runs on trackage often shared with intercity rail and freight trains, typically serving newer suburbs and rural areas. Commuter rail trains are typically built to higher standards, as they run at higher speeds are at risk of more severe crashes. This distinguishes commuter rail from interurbans, which use light-rail vehicles on tracks through lower density areas.

Bus

A bus shares many characteristics with light rail, but does not run on rails. Trolleybuses are buses that are powered by overhead wires. Railbuses, vehicles that can travel both on rails and on roads, have been tried experimentally, but are not in common use. The term bus rapid transit is used to refer to various methods of providing faster bus services, but the systems which use it are usually more equivalent to light rail than to rapid transit. Some cities experimenting with guided bus technologies, such as Nancy have chosen to refer to them as 'trams on tyres' (rubber tyred trams) and given them tram-like appearances.

References

For terminology, see passenger rail terminology.
* [http://flyvbjerg.plan.aau.dk/Publications2007/URBANRAIL61PRINT.pdf Flyvbjerg, B. "Cost Overruns and Demand Shortfalls in Urban Rail and Other Infrastructure," Transportation Planning and Technology, vol. 30, no. 1, February 2007, pp. 9-30.]

External links

* [http://www.nautf.com NAUTF | North American Urban Transit Forum]
* [http://www.eastsiderailnow.org/myths.html Rail Transit Myths -- And Realities]
* [http://metrobits.org metrobits.org world metro database]