Signalling on LUL


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The Development of Signalling on the London Underground

Piers Connor

from Evolution of Modern Traction Seminar on 5th November 2005

This presentation recalled that the London Underground railways were in the forefront of signalling development in the UK and were one of the earliest users of automatic signalling, starting in 1903 on the District Railway.  The system was imported from the US.  It provided fully automatic signalling on most of the railway away from junctions.  Track circuits detected the presence of trains in each block and held the signal at danger until the block was clear.  The normal aspect of the automatic signal was clear as opposed to the traditional, manually controlled signals which normally show stop until specially cleared for a train.

At junctions on the London Underground, the same principles of automatic train detection applied but signals were equipped with lever-operated controls in a signal cabin to allow routes to be set and trains to be regulated.  The principles have remained to this day but with single, line control centres replacing large numbers of signal cabins.

New automatic signalling was installed on all District owned lines and the LER tube lines between 1904 and 1907.  Semaphore signals were standard for open sections.  In tunnels, the District used semaphores (some locations having shortened arms where space was tight) and the tube lines used fixed, oil-lit lamps with a vertically moving spectacle plate to change the aspect seen by the driver.  The oil lamps were later replaced by electric lamps.  The first, outdoor, colour light signals used on the Underground were introduced on the Edgware extension in August 1924.  Later, all the mechanical signals were replaced, the last going in 1953.

The Metropolitan only gradually went over to automatic track circuit operated signals.  They started on the Circle in 1908 and it took them until 1919 to complete it.  They got to Harrow by 1911 finally completed the H & C in 1929.  In 1930 the Uxbridge branch got track circuits and the semaphores were replaced by 3-aspect colour lights.

Route lights were first seen on the Underground shortly before World War II on the Stanmore branch.  The idea was derived from the Southern Railway, who used it from the early 1930s.  Junction signals in tunnels use a miniature version of harbour lights or, for more recent versions, a strip of white light at the appropriate angle.

In the mid 1930s, the Underground introduced route setting and a relay interlocking was installed at Wood Green.  After the second world war, a remote control frame was introduced at Ealing Broadway.  In the mid 1950s, programme machines were introduced on the Northern Line, allowing automatic route setting according to a pre-set timetable.

In the early 1960s, automatic train operation experiments started and led to the opening of the first ATO railway in the world, the Victoria Line.  ATO has also been installed on the Central Line.

Finally, the presentation told how, in the future, the Victoria Line and sub-surface lines will get distance-to-go signalling and the Northern and Piccadilly Lines will get an updated version of the automated system used on the Docklands Light Railway.