The first underground railways were those used in mines, with small trucks pushed by hand or, later, drawn by ponies, running first on wooden, then iron, and finally steel rails. Once the steam railway had arrived, however, thoughts soon turned to building underground passenger railways, or subways, to avoid the traffic congestion which was occurring in city centers in the middle of the nineteenth century.
This problem was most apparent in old, established cities, and the first passenger underground railway was opened in London, England, in 1863. This was the Metropolitan Railway, 3.75 miles (6 km) long, which ran from the main line railway terminal at Paddington to Farringdon Street in the business area of the City of London. Steam locomotives were used and the track was built to the broad 7 ft (2.13 m) gauge of the Great Western Railway who supplied the rolling stock — though subsequently the standard gauge was adopted. Some of the trains ran through from suburban stations on the Paddington main lines, but there was also a purely local service. The line was soon carrying over 27,000 passengers a day and further undergroundlines soon followed in London. Other European cities such as Budapest, Hungary; Berlin, Germany; Glasgow, Scotland; and Paris, France, also developed subway systems, followed later by cities in the rest of Europe, North and South America, Russia and Japan. Subway lines have continued to be built throughout the twentieth century, both as extensions to existing networks and as complete new systems for city center transportation. In many cases the underground sections join up with surface or elevated lines in the surburban areas to give an integrated Metro or Rapid Transit System.
In some cities the introduction of subways was delayed by the presence of alternative transportation systems such as streetcars and light railways. In New York, the “Elevated” railway running down the center of the streets started working in 1872. Despite its success, the advantages of underground systems were such that by the turn of the century it was decided to start work on the New York Subway. From the outset the subway was treated as an integrated system, and the original route – the Broadway and Fourth Avenue Line –was put into service in 1904. Advantage was taken of experience gained from the “Elevated” and from studies of the London Underground to produce a flexible layout, with one of the major features being the decision to have multiple tracks. On systems such as the London Underground most of the lines have two tracks, for up and down services respectively, and the trains follow one another with stops at all stations. With the New York Subway, however, there are three or four tracks, and it is therefore possible to run express services that bypass some of the stations on the network.