A tram (in North America streetcar or trolley) is a rail vehicle that runs on tramway tracks along public urban streets; some include segments of segregated right-of-way. The lines or networks operated by tramcars as public transport are called tramways or simply tram/streetcar. Historically the terms electric street railways and trolley (not meaning trolleybus) were also used in the United States. In the United States, the term tram has sometimes been used for rubber-tired trackless trains, which are unrelated to other kinds of trams.
Tram vehicles are usually lighter and shorter than main line and rapid transit trains. Today, most trams use electrical power, usually fed by a pantograph sliding on an overhead line; older systems may use a trolley pole or a bow collector. In some cases, a contact shoe on a third rail is used. If necessary, they may have dual power systems—electricity in city streets and diesel in more rural environments. Occasionally, trams also carry freight.
Trams are now commonly included in the wider term "light rail", which also includes grade-separated systems. Some trams, known as tram-trains, may have segments that run on mainline railway tracks, similar to interurban systems. The differences between these modes of rail transport are often indistinct and a given system may combine multiple features.
One of the advantages over earlier forms of transit was the low rolling resistance of metal wheels on steel rails, allowing the trams to haul a greater load for a given effort. Problems included the high total cost of ownership of horses. Electric trams largely replaced animal power in the late 19th and early 20th centuries. Improvements in other vehicles such as buses led to decline of trams in the mid 20th century. However, trams have seen resurgence in recent years.