The history of traffic signals in the UK

Did you realise traffic signals pre-date motorised vehicles?

“A lot of people are surprised to find out that the history of traffic signalisation pre-dates the advent of motorised vehicles.

image of a green traffic signal aspect

The technologies that lie at the root of this actually emanate from research work undertaken by the British Admiralty, in two particular fields:

Communications - To enable the Admiralty in London to communicate quickly with the naval ports along the south coast of England, a chain of optical telegraph stations were erected in the late 18th century. The operation of the telegraph was further improved by work undertaken by General Pasley in the early 19th century, who observed the system perfected in France by Claude Chappe, which resulted in the adoption of the Semaphore style of telegraph from 1816 in the UK.

In later life, General Pasley became Inspector General of Railways and during this time, in response to rising accident rates, suggested the use of the Semaphore signal as a means of improving communication with locomotive drivers. The first of these was erected by Charles Gregory of the London and Croydon Railway at New Cross in 1842.

Navigation - With the introduction of steam ships in the mid-19th century, there was a huge increase of collisions at sea, resulting in many ships being lost. Following the work of a Parliamentary Select Committee which first looked at the issue in 1831, a number of studies were carried out. These included investigating the use of coloured lights to make the direction a ship is travelling in more apparent to other vessels after dark. It was found that oil lamps with clear, red and green lenses could be viewed from the greatest distance, with minimal risk of misinterpretation. The outcome of this study was the recommendation that red and green lights should be used as navigation sidelights on vessels, which were adopted universally in 1858.

These two bodies of work, which were leading edge technologies at the time, resulted in two sets of developments:

  • The widespread adoption of Semaphore signals to control traffic on the railways
  • The use of red and green lights as visual warning signals
image of the first traffic signal anywhere in the world, Bridge Street, London, December 1868

Highway Signals - In the mid-19th century, traffic congestion in London was getting worse and, in response to a suggestion made by a Parliamentary Select Committee, the first traffic signal in the world was installed in Bridge St, adjacent to the Houses of Parliament, in December 1868. This was undertaken to enable MPs to cross over this busy street. The signal, which was promoted by railway engineer J P Knight, who lived nearby in Bridge Street, was over 20 foot high. When the semaphore arm was extended horizontally it meant ‘stop’, and when lowered to 45° it meant ‘proceed with caution’. At the top of the pole were red and green gaslights, which were used to augment the arm at night. The operation of the signals was controlled manually by a police officer turning a handle. Unfortunately, the signal didn’t last for long because on 2 January 1869, leaking gas in the signal caused it to explode. The police operator was injured in the incident, resulting in the installation being removed.

After this, the only other recorded traffic signal installation in the UK was part of the bridge interlocking system which controlled the lifting operation at Tower Bridge. The system was designed and manufactured by the railway signal firm of Saxby and Farmer, who had also made the earlier signal at Bridge Street. Included in the system were semaphore signals (also fitted with green and red gas lights) for both river and highway traffic, which worked in relation to the operation of the current bridge position. Part of the mounting bracket for the original signal is still visible today. Since opening in June 1894, the traffic signals have continued to control traffic flow on the bridge which arguably makes Tower Bridge the oldest signalised location in the world.

No further attempts seem to have been made at mechanised traffic control, until the growth of motorised traffic in the U.S. lead to a need to control junctions in the early 20th century. A plethora of differing signal systems were developed over the coming years, but these mainly fell into two families, semaphore arms and light signals. One of the most famous of the semaphore type of signal was patented in 1922 by inventor Garrett Morgan. His signal consisted of rotating arms, red and green lights and a bell (which warned of an impending change). Although this system was hand-cranked, it had the added sophistication of including an all-stop period between opposing traffic streams to allow the junction to clear. However, it soon became apparent that semaphore styles signals were an evolutionary dead end.

The first electric traffic light was invented by Lester Farnsworth Wire and installed in Salt Lake City in 1912. Lester was the head of the traffic division of the Salt Lake City Police Department. His signal had two lamps, one red and one green, and was installed in a large wooden box with two six-inch holes on each side. It was operated by a patrolman who used a two way switch to change the light’s colours. However, in this instance, the same signal was displayed to all approaches. The colour it illuminated (red or green) signified traffic could flow on a particular approach, i.e. north and southbound or east and westbound. William Potts, a Detroit policeman, invented the first three-colour lights in 1920. His four-way signal head used railway signal lamps and was designed to be suspended over the centre of a junction to control traffic from four approaches. It was the first signal to resemble the operation we know today.

image of manually controlled electric traffic lights installed in Piccadilly, London, 1925

In England, the first manually controlled electric traffic lights were installed in Piccadilly, London, in 1925 and the first automatically controlled signals were installed in Princes Square, Wolverhampton in 1927. Today, this junction has specially painted black and white signal poles to commemorate its historic significance.

During the 1930’s, experiments were carried out in the use of vehicle actuation to make the traffic signals responsive to vehicles using a junction. An early attempt at this utilised a microphone placed at the side of the road, which would make the lights respond to motorists sounding their horns. Although this system worked, it was very unpopular with people living nearby!

Later experiments used electrical pressure mats and pneumatic tubes. These were extensively used up to the 1970’s when they were replaced with inductive loops for permanent installations; although they are still used for temporary count sites where they are fitted to the surface of the carriageway.

The first vehicle actuated site in the UK was installed in 1932, at Gracechurch St / Cornhill in London. Unfortunately, history repeated the events of 1869 when the controller blew up. In this case though, gas had seeped into the controller cabinet, through the underground cable ducts from a nearby leaking gas main, and was sparked by the electrical apparatus in the controller. The good news is, on this occasion, the accident did not block the course of progress and within a couple of year’s vehicle actuated controllers were being used widely across the country.

image of the first vehicle actuated site in the UK, installed in 1932, at Gracechurch Street by Cornhill in London