The New York subway runs above ground for 40 percent of its length
New Yorkers call their whole system the subway, yet around 40 percent of it runs above street level. The name itself was borrowed from London, where a line opening in 1890 was going to be called the City and South London Subway. In most of Britain today, though, a subway just means a pedestrian underpass.
Rapid transit began with London's Metropolitan Railway in 1863, partly underground and hauled by steam engines. Riding through smoky tunnels was unpleasant even with ventilation, and experiments with trains pushed by air pressure never caught on in cities. New York tried another route in 1868 with an elevated line pulled by cables from stationary steam engines. The real breakthrough came with the City and South London Railway of 1890, the first electric rapid transit line and fully underground, and three years later Liverpool opened an overhead railway designed for electricity from the start.
What a system is called often depends on where it runs through the city centre. Tunnels produced names like the Underground, the German U-Bahn and Stockholm's tunnelbana, while viaducts gave Chicago its L and Vancouver its SkyTrain. Hong Kong uses MTR, much of Southeast Asia says MRT, and Boston simply says the T. In New York the L refers to one particular line on 14th Street, not elevated trains in general.
Size varies from the tiny to the enormous. Serfaus, a small car-free village in the Austrian Tyrol, runs a short U-Bahn line of its own, while Zurich, Switzerland's largest city, voted down a U-Bahn in a 1970s referendum and expanded its suburban rail instead. At the other end, China had 40 systems with over 4,500 kilometres of track by 2021 and drove most of the world's metro growth in the 2010s. Beijing and Shanghai run the longest and busiest networks.
Metro lines have their own right of way that no pedestrian or car can enter. Stations usually have high platforms level with the train floor, so vehicles are built to measure. Many lines split into branches in the suburbs, letting trains run more often through the centre.
Source: Rapid transit
