rail · self-propelledstreet-level

Tram / Light Rail

rails in the street

Rails set into the pavement, an electric car sliding along them, and a wire overhead feeding it power — the tram is the oldest surviving idea in urban rail, and one that never fully went away. It is also a spectrum, not a single thing: at one end a single car nosing through car traffic, at the other a multi-car train that is a metro in all but name.

How it works

A tram is an electric rail vehicle running on tracks laid mostly at street level. Power comes from an overhead wire, collected by a pantograph (a sprung frame that presses up against the wire) or, on older systems, a trolley pole. Current runs down through the traction motors and returns through the running rails. A few modern lines hide the wire entirely, using ground-level power rails energized only under the car, or onboard supercapacitors charged at each stop — cosmetic solutions for historic city centers that dislike overhead cabling.

The spectrum: streetcar to light rail

There is no hard boundary here, only a slider. At the light end sits the streetcar: usually a single car sharing lanes with cars and buses, stopping at the curb, waiting at ordinary traffic lights. Push toward the heavy end and you get light rail (LRT):

Segregated right-of-way — its own reserved lane, median, or trackbed instead of mixed traffic.
Multi-car trains — two to five coupled vehicles running as one, where streetcars run solo.
Signal priority and higher speeds — fewer conflicts with road traffic, so faster and more reliable.

Wikipedia's own framing: a tram is a type of light rail, distinguished by tighter integration into streets, lower signal priority, coexistence with cars, and lower capacity. "Streetcar" and "light rail" are two readings of the same dial.

Where it blurs into a metro

Keep pushing and light rail approaches a metro. The dividing line is grade separation. A metro runs entirely on fully independent track — tunnels and viaducts, no level crossings, no shared pavement. Light rail is a mix: some fully separated segments, some reserved track with the occasional level crossing, some plain street-running. That flexibility to slide between environments in a single line is exactly what a metro cannot do — and exactly why the tram/metro line stays fuzzy.

A history of dying and coming back

Trams began as horsecars in the 1830s, then went electric: the first permanent public electric tramway opened at Gross-Lichterfelde near Berlin in 1881. Electric trams spread through nearly every sizable city by 1900. Then came the mid-century decline — the automobile, cheaper buses, and in the US the notorious streetcar dismantling — which stripped systems out of most American cities. Since the 1980s the mode has returned as modern LRT, and today's cars are typically articulated, low-floor designs: a flat step-free interior at platform height, regenerative braking that feeds power back to the wire, and a walk-through body that flexes around curves. The oldest idea in city rail, rebuilt for accessibility.