This week, or next, depending on which date you care to choose marks the 150th anniversary of the world’s first purpose built traffic light.

Cars didn’t exist in 1868, this was to control horses — or more accurately, control the humans on the carts and omnibuses who told horses what to do.

Towering around 20 feet above the carriageway, the first traffic light resembled a railway signal with waving arms to indicate stop. It included the familiar red and green lights, light by gas lamps, but not amber, and required police constables to change the light manually using switches.

The arrival of the traffic signal was in response to a suggestion made by a Parliamentary Select Committee which worried about the dangers of crossing the busy street outside Parliament. That wasn’t just a localised issue, as in 1866, 1,102 people were killed and 1,334 injured on roads in London, prompting calls to do something to improve road safety.

The signal, which was designed by railway engineer J P Knight, who lived nearby in Bridge Street, and supplied by the railway signalling manufacturers, Saxby and Farmers.

The signal was installed outside Parliament around the 7th-10th December. However, it wasn’t used until the following Thursday — the 17th December, when Parliament returned following the recent General Election, so that could be the date to choose, as that’s when the traffic signal was put into use for the first time.

Described as a “handsome iron pillar” it contained three 4-foot long semaphore arms, two barring traffic between the bridge and Great George Street and the third for traffic turning to the bridge from Parliament Street. It was designed to accept a fourth semaphore arm, but that was never added.

When the movable arm was extended horizontally, that signaled “stop.” When the movable arm was at a 45-degree angle, that signaled “caution.” Then at night, the red and green gas lights supplemented the arms to signal “stop” (red light) or “caution” (green light).

It’s notable that the green light was described as caution, whereas today the green light is often a trigger to hit the accelerator as fast as possible.

Enamel signs were also put up around the area to explain how the traffic signal worked.

Despite much press attention at the time of its installation, and hope that many more would soon follow it, the huge signal suffered a set back on 2nd January 1869, when a policeman was seriously injured when leaking gas from the signal exploded. It seemed to be in use for a short while afterwards, but was eventually removed.

With the exception of an automated signal at Tower Bridge which was linked to the bridge opening, traffic lights did not return to London until 1926, when a manually operated light was installed in Piccadilly.

Despite it’s short life, and the long hiatus before anyone tried again, this is still considered to be the very first traffic light in the world. Right here in London.

A green memorial plaque to J.P. Knight can be seen on the corner building next to where the original traffic lights would have been erected, and where traffic lights today still let people cross the road.



Traffic Signals: An introduction to signalised junctions and crossing facilities in the UK

London Evening Standard – Tuesday 08 December 1868

Cork Examiner – Friday 11 December 1868

Cambridge Chronicle and Journal – Saturday 26 December 1868


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