Definition: Single Track / Double Track

Heritage streetcar lined can be built with either single track—one track shared by cars operating in either direction—or double track—a separate track for each direction. If single track construction is used, then there need to be periodic passing sidings where a car traveling in one direction can wait while one going in the opposite direction passes (see photos).

Single track construction is considerably cheaper to build but has lower capacity as the number of cars operating in each direction is limited by the spacing of passing sidings. Also, on narrow streets where streetcars will share the pavement with auto traffic, it may not be possible to place a single track in the middle of the street as there may not be room for autos to pass on either side of a streetcar in the middle.

Double track construction costs are higher than for single track, but the capacity is much higher as streetcars traveling in opposite directions may pass at any point. However, the right of way to be used—whether in street or away from a street—has to be wide enough to accommodate both tracks.

Thus available space, anticipated traffic, and funding available will be key components in deciding whether to use single or double track.

A classic passing siding on the last urban single track streetcar line in America: route 65 in Pittsburgh, abandoned in the mid-1960s.	A contemporary passing siding on Tampa's heritage line, opened in October 2002, but featuring left hand operation.

Left Hand / Right Hand Operation

Normally, as streetcar lines often share rights-of-way with auto traffic, streetcars on double track sections or passing sidings will operate to the same side as auto traffic. In other words, in North America, most of South America, or Europe, streetcars will operate on the track to the right. In the United Kingdom, Ireland, Australia or most Commonwealth countries, they will operate on the left track in keeping with the local rules of the road.

By having streetcars follow the same rules as road traffic, even on sections where they are separated from auto traffic, motorists and pedestrians will "know" on which track to expect a car to approach. This practice improves safety.

However, occasionally, streetcar operating organizations may choose to operate cars on the opposite tracks at passing sidings for special reasons, such as aligning doors on single sided cars to a platform between the tracks. Such exceptions are infrequent and should be considered carefully as the safety risk counter-intuitive operation poses to the public should be carefully weighed versus the anticipated savings.