In the 1860s London was the largest city in the world, with 3 million people squeezed into an area much, much smaller than the present-day city. This high population density caused many problems. These ranged from epidemics of infectious diseases, to pollution from the six million tons of coal that were burned each year, and squalid and overcrowded slum housing.
One of the most obviously visible problems was traffic. The motor car had yet to make an appearance, but the streets were filled with hundreds of thousands of horse-drawn carts, carriages and buses. Traffic jams were a constant problem and were at their worst around the bridges that crossed the River Thames, which created bottlenecks. The lack of control over the traffic made it dangerous as well. Over 1000 people were killed and more the 1300 injured on London’s roads in 1866.
A year earlier, in 1865, a 36 year-old engineer, John Peake Knight, had contacted the Metropolitan Police with an idea. He was Superintendent of the South Eastern Railway and thought it should be possible to use signals, like those used on the railways, to control and improve the flow of traffic.
As ever the idea took a while to be developed but by the end of 1868 a prototype system was ready. It was installed on the north side of Westminster Bridge, close to the Houses of Parliament and Big Ben. The system used railway style semaphore arms to indicate when traffic should stop and when it could go. At night the arms were replaced with gas powered lights. The lights also followed the colour coding system used on railways, red for stop and green for go. These were the first traffic lights anywhere in the world.
Because it was a totally new concept for road users, posters were put up near the signals explaining how the system worked. There was no way of automating the system, so a policeman had to stand next to the signals to operate them – not a great job in the depths of winter. The signals went into operation on 9th December 1868.
The system caused an immediate improvement in traffic flow, and John Knight was confident that more sets of signals would be installed in other London traffic hot spots. Then disaster struck. In early January 1869 the gas supply developed a leak and one of the lights exploded, leaving the policeman operating them with a badly burned face. At this point the system was considered too dangerous for further development and whole project came to sudden and disappointing end.
It would be nearly sixty years before the next traffic lights were installed in London. In 1925 a set using safer electric lamps went into use near Piccadilly. As anyone who drives in London can testify, quite a few more sets have followed since.