Wikipedia:Very good articles/Kingsway tramway subway
The Kingsway tramway subway is a cut-and-cover Grade II Listed tunnel in central London. In 1898 it was decided to demolish the slum districts in the Holborn area and rebuild it. This gave a chance to use the new streets for a tramway that would connect the lines in the north and south. This new tramway was built by the London County Council who decided to build the route as an underground connection. The tunnel originally opened for use by single deck tramcars only, but an upgrade between 1929 and 1931 meant that double deck trams could later use it. The subway was closed in 1952. Part of the subway is now the Strand underpass, but it is largely untouched and still has tram tracks inside it.
The London County Council had two tramway systems called the "North Side" and "South Side". For a long time they wanted to join the two together. This would allow them to send trams from the "North Side" to the Central Repair Depot in Charlton in South East London for overhauls. In 1902, the Council decided to build a tramway that was under the ground (subway). The subway went from Theobalds Road in the north to the Embankment underneath Waterloo Bridge to the south. From there a line that was not underground would continue over Waterloo Bridge.