In 1900, a pioneering underground railway began running in London.
The Central London Railway (CLR) was given permission in 1891 for a tube line between Shepherd's Bush and a station at Cornhill, and the following year an extension to Liverpool Street was authorised. The line was built following the streets above rather than running underneath buildings, because purchase of wayleave under private properties would have been expensive, and as a result one line runs above another in places, with platforms at different levels at St Paul's, Chancery Lane and Notting Hill Gate stations. The tunnels were bored with the nominal diameter of 11 feet 8 1/4 inches (3.562 m), increased on curves, reduced to 11 feet 6 inches (3.51 m) near to stations. The tunnels generally rise approaching a station, to aid braking, and fall when leaving to aid acceleration.
The line between Shepherd's Bush and Bank was formally opened on 30 June 1900. With a uniform fare of 2d the railway became popularly known as the Twopenny Tube. It was initially operated by electric locomotives hauling carriages, but the heavy unsprung locomotives caused considerable vibration in the buildings above the line and the railway changed to using electric multiple units by 1903.
In July 1907, the fare was increased to 3d for journeys of more than seven or eight stations. The line was extended westwards with a loop serving a single platform at Wood Lane for the 1908 Franco-British Exhibition. A reduced fare of 1d, for a journey of three or fewer stations, was introduced in 1909 and season tickets became available from 1911. The extension to Liverpool Street opened the following year, providing access to the Great Eastern station and the adjacent Broad Street station by escalators. The Central London
