Haulage and Infrastructure
Given the small dimension of the tunnels, steam power, as used on London's other underground railways, was not feasible for a deep tube railway. Like Greathead's earlier Tower Subway, the CL&SS was intended to be operated by cable haulage with a static engine pulling the cable through the tunnels at a steady speed. Section 5 of the 1884 Act specified that:
- "The traffic of the subway shall be worked by ... the system of the Patent Cable Tramway Corporation Limited or by such means other than steam locomotives as the Board of Trade may from time to time approve".
The Patent Cable Tramway Corporation owned the rights to the Hallidie cable-car system first invented and used in San Francisco in 1873; trains were attached to the cable with clamps, which would be opened and closed at stations, allowing the carriages to disconnect and reconnect without needing to stop the cable or to interfere with other trains sharing the cable. There were to be two independent endless cables, one between City station and Elephant and Castle moving at 10 mph, and the other between Elephant and Castle and Stockwell, where the gradient was less, at 12 mph. However, the additional length of tunnel permitted by the supplementary acts challenged the practicality of the cable system.
It is reported that this problem with the CL&SS contributed to the bankruptcy of the cable company in 1888. However, electric motor traction had been considered all along, and much engineering progress had been made since the tunnel's construction had begun in 1886. So, CL&SS chairman Charles Grey Mott decided to switch to electric traction. Other cable-operated systems using the Hallidie patents continued to be designed, such as the Glasgow Subway which opened in 1896.
The solution adopted was electrical power, provided via a third rail beneath the train, but offset to the west of centre for clearance reasons. Although the use of electricity to power trains had been experimented with during the previous decade, and small-scale operations had been implemented, the C&SLR was the first major railway in the world to adopt it as a means of motive power. The system operated using electric locomotives built by Mather & Platt collecting a current at 500 volts (actually +500 volts in the northbound tunnel and -500 volts in the southbound) from the third rail and pulling several carriages. A depot and generating station were constructed at Stockwell. Owing to the limited capacity of the generators, the stations were originally illuminated by gas. The depot was on the surface, and trains requiring maintenance were initially hauled up via a ramp although, following a runaway accident, a lift was soon installed. In practice, most rolling stock and locomotives went to the surface only for major maintenance.
To avoid the need to purchase agreements for running under surface buildings, the tunnels were bored below roadways, where construction could be carried out without charge. At the northern end of the railway, the need to pass deep beneath the bed of the River Thames and the mediaeval street pattern of the City of London constrained the arrangement of the tunnels on the approach to King William Street station. Because of the proximity of the station to the river, steeply inclined tunnels were required to the west of the station. Because of the narrow street under which they ran, they were bored one above the other rather than side by side as elsewhere. The outbound tunnel was the lower and steeper of the two. The tunnels converged immediately before the station, which was in one large tunnel and comprised a single track with platforms either side. The other terminus at Stockwell was also constructed in a single tunnel but with tracks on either side of a central platform.
Read more about this topic: City And South London Railway