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This article describes subways as mass transit lines. For other uses see subway (disambiguation).
Subway describes a rapid transit line that is at least partly underground. Subway also describes an actual underground structure or tunnel used by mass transit vehicles.
The term is most commonly used in the U.S. and Canada, though the term is also used elsewhere, such as to describe the subway line in Glasgow, Scotland and in translation of system names or descriptions in some Asian cities into English.
The term is roughly equivalent to the term metro in many other locales.
Physical description
Strictly speaking, a subway is an underground line designed for use by usually electrically-powered rapid transit cars for urban transit and containing stations spaced at more-or-less regular intervals for the receipt and discharge of passengers.
Subways are usually built by tunneling or cut-and-cover construction, the latter of which involves opening a trench, constructing steel infrastructure, and then covering the completed line with a roof and roadway or other surface treatment.
Generic use
Lines involving physical subways tend to be described as subway lines whatever their physical characteristics. In the New York Subway the system is known as "the Subway" despite the fact that most lines outside of Manhattan Island do not operate in actual subways. Elevated "subway" lines on a steel infrastructure are most common there, though other subway lines may be built on reinforced concrete structures called viaducts, on earthen embankments, in open cuts (trenches), on bridges or the ground surface.
An opposite usage is in Chicago, where the entire system is known as "the 'L' " (for eLevated) despite having surface and highway median sections, and two physical subways in the Loop area.
Typical equipment
Subway equipment, no matter the right-of-way it uses, are almost exclusively electrically-powered cars operated by multiple-unit train control and are dedicated to subway service. They have floor-level platforms and multiple doors spaced along the car side for quick loading and discharge.
Variant usage
Some lines described as subway lines use light rail or trolley equipment. Notably, the Newark City Subway, about half underground, is one of these. Some times the term is qualified, such as in Philadelphia, where trolleys operate in an actual subway for part of their route and on city streets for the remainder. This is locally styled subway-surface. The Brussels Metro has three traditional heavy rail lines and two "premetro" lines which run trolleys but have enough width to be eventually converted to the bigger metro standards if the traffic warrants it.
Bus subways are uncommon but do exist, though in these cases the non-underground portions of route are not called subways. Newark, New Jersey, had a bus subway with two stations inherited from the streetcar system. Seattle, Washington has a bus subway downtown, in which dual-fuel buses can operate on overhead wires when in the subway and via internal combustion when outdoors.
See also
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