A tram (also known as a tramcar; a streetcar or street car; and a trolley, trolleycar, or trolley car) is a rail vehicle which runs on tracks along public urban streets (called street running), and also sometimes on separate rights of way. Trams powered by electricity, which were the most common type historically, were once called electric street railways. Trams also included horsecar railways which were widely used in urban areas before electrification.
Trams may also run between cities and/or towns (for example, interurbans, tram-train), and/or partially grade separated even in the cities (light rail). Trams very occasionally also carry freight.
Tram vehicles are usually lighter and shorter than conventional trains and rapid transit trains. However, the differences between these modes of public transportation are often indistinct. Some trams (for instance tram-trains) may also run on ordinary railway tracks, a tramway may be upgraded to a light rail or a rapid transit line, two urban tramways may be united to an interurban, etc.
Most trams today use electrical power, usually fed by an overhead pantograph; in some cases by a sliding shoe on a third rail or trolley pole. If necessary, they may have several power systems. Another power source is diesel oil; a few trams use electricity in urban streets, and diesel in more rural environments. Steam, petrol (gasoline), gas and draft animals have historically been used as power sources. Horse and mule driven trams do still occur, mostly for the tourist trade. Certain types of cable car are also known as trams.
Azienda Trasporti Milanesi (ATM) is a public company, responsible for public transportation in Milan city and some surrounding municipalities, in Italy. It operates 18 tram lines, part of which are run with Peter Witt streetcars from the 1920s, 82 urban Bus lines, 4 Trolleybus lines, 35 interurban Bus lines, 4 underground lines (Metropolitana di Milano), carrying over 734 million passengers in 2010.
ATM offers also other minor services mainly related to transportation around the city. These services include Radiobus, an on-call minibus service; the light railway linking the San Raffaele Hospital with the line 2 underground; the Como–Brunate funicular railway; Guidami car sharing and BikeMibike sharing services.