The world’s first set of traffic signals was installed in London in December 1868. It stood outside the Palace of Westminster, towering over the junction between Bridge Street and Parliament Street.

It is no accident that this world-conquering machine should have had its genesis here. In the 1860s, London was by far the biggest city on the planet, with a population close to four million. It was the world’s leading financial centre, the world’s biggest port, and the hub of a vast empire that stretched from Canada to Australia.

London was also a victim of its own success. Its streets teemed with pedestrians, horses, omnibuses, cabs and carts, all vying for the same space. Traffic jams were common in its narrow, medieval streets, and fatal accidents were on the increase: between 1858 and 1860, according to a debate in the House of Lords, the rate at which pedestrians were killed on the city’s roads had already reached one a week. Within three years that rate had almost doubled; three years later it doubled again. Thousands more pedestrians had been permanently maimed by being knocked down or run over by reckless drivers.

In an effort to bring order to the chaos, Parliament appointed a House of Lords Select Committee to draw up new traffic regulations for the city. In 1866, this committee gathered together all the experts it could find – scholars, engineers, businessmen, cab drivers, policemen and so on – and began asking for ideas. It was not long before proposals came flooding in. Some people suggested that delivery drivers should be banned from the city centre at peak hours. Others demanded that cab drivers should be made to carry lamps after dark, so that pedestrians could see them coming. Proposals were put forward for safer carriages, fewer street traders, more sweeping police powers. And each proposal was discussed and debated by the politicians over the following year.

The idea for traffic lights came from a 38-year-old railway superintendent called John Peake Knight. According to Knight, the solution to London’s problems was simple: all the city needed was a decent signalling system. Major junctions were already regulated by traffic policemen – but it was dangerous work, and the policemen were not always visible in the throng. What Knight proposed was a system like the one already in use on the railways: semaphore signals attached to the top of tall posts and augmented with coloured lights that were visible even after dark. Signals like these could still be operated by policemen, but without the need for them to stand in the midst of dangerous traffic.

After much debate, the committee decided to give Knight’s idea a try. A prototype was manufactured by Messrs Saxby and Farmer, a firm of railway engineers, authorised to erect it in the street outside the Houses of Parliament. If the signals worked there, the trial would be extended to other parts of the city.

So it was that the world’s first traffic light came to stand at the very heart of empire. This ‘gigantic signalling apparatus’, as The Times called it, was far more imposing than any policeman. At a height of 24 ft, with two huge semaphore arms at its sides, it loomed out of the London fog like some kind of supernatural apparition. When its arms were fully raised they stood more than eight feet across, commanding the traffic below to halt.  At the same time, a red light on its head would glare down at London cabbies and delivery drivers. For a minute or so, protected by this mechanical beast, pedestrians would be free to cross the road; until the semaphore arms were lowered again, the red light turned to green, and the traffic was finally released from its spell.

The Bridge Street semaphore was used for the first time on Thursday 10 December 1868 – the first day of the newly elected Parliament – shepherding lords and commoners to safety beneath its beneficent glow. By all accounts, those who first used it were delighted. In recent months, two MPs had been knocked down on this street: with the new signal in place, it seemed that the rulers of the empire might at last be able to reach their hallowed halls without fearing for their lives.

Unfortunately, the triumph of this new invention was short-lived. At the beginning of January, just three weeks after it had been installed, the base of the structure exploded. An investigation concluded that a leaking pipe must have filled the hollow pillar with a column of gas, which had ignited as soon as a police officer had opened the little door at the bottom to switch the light off for the night. A jet of flame had been hurled out of the semaphore straight into the policeman’s face. The semaphore had to be repaired, and the policeman had to be treated for severe burns.

Just as worrying was the way that drivers often ignored the stop signal, ploughing on through the street junction even when pedestrians were cleared to cross the road. It seems that some drivers passing down this street either didn’t know what the semaphore meant or didn’t care. Even those who understood that they were supposed to stop when the semaphore arms were outstretched were often confused when its arms were angled downwards at 45 degrees (a signal that meant that they should proceed, but only with caution). As a consequence, pedestrians remained in danger: the new system was simply lulling them into a false sense of security.

In March, a question was asked in the House of Commons about whether the new semaphore was indeed conducive to public safety, or whether it shouldn’t be removed. The Home Secretary, Henry Bruce, did his best to defend it, claiming that his senior police officers were ‘strongly impressed with its advantages’, but its general ineffectiveness, coupled with constant mechanical breakdowns, meant that it soon fell into disuse. Eventually, it was made redundant by structural works around this junction, including a subway. By the beginning of 1871, commentators were calling it a ‘beautiful ruin’. Its arms were now motionless and its gaslight unlit.

That March, a poignant letter appeared in The Times newspaper, purporting to be from the semaphore itself. ‘Will some kind MP ask why I am compelled to stand still all the day long at the crossroads?’ it asked. ‘I feel I am not useful, and no art critic has yet discovered that I am ornamental. Nobody owns me; my arms ache from being so long in one position, and my head is cold from the draughts in all directions.’

A year later, on 19 January 1872, The Times printed a second letter from the semaphore. ‘I really am not fit to be seen,’ it lamented. ‘I do nothing, either by day or night. I don’t think I do much harm, though some ill-natured persons say I frighten the babies, but I know I do no good. You were good enough, Sir, to insert a letter from me long ago, asking for removal, if not for decent burial. Another year has passed, and I still cumber the ground. Please, Sir, ask them to have pity on me…’

In the coming months, the Bridge Street semaphore was at last put out of its misery. It was taken down and carted away for scrap. The streets of London would not be illuminated by traffic lights again for more than half a century.

Not long after the Bridge Street semaphore was frightening babies in London, another new invention began to take off across the world. The motor car, first patented by Karl Benz in 1885, would transform our city streets. In the US, particularly, automobiles rapidly replaced the horse-drawn carts and carriages that had been the only form of transport since time immemorial.

Directing this traffic was an extremely dangerous and unpleasant job. Police officers had to stand in the middle of busy intersections in all weathers. They were often overwhelmed by the sheer volume of traffic hurtling around them.

Step forward a young police sergeant in Salt Lake City, named Lester Wire. As the head of the city’s first ever traffic squad, Wire wanted to bring order to the chaos and make working conditions for his men safer, too. So he concocted an idea that would solve both problems at once. Rather than have his men directing the traffic with their arms, he would rig up a system of lights, wired up to the electric trolley car system. The lights would be up above the street where everyone could see them clearly: red for ‘stop’ and ‘green’ for go. The policeman who controlled these lights would also be high above the traffic, sitting in a signal box that looked like a birdcage on top of a pole. Here he could sit in comfort, safe from both the traffic and the weather, conducting events down below with the mere flick of a switch.

Wire’s first ‘bird-cage’ appeared in Salt Lake City in 1912 at the intersection of Main Street and 200 South. After that, new inventions came thick and fast. The first patented traffic-light system was installed in Cleveland, Ohio in August 1914. The first interconnected system across many junctions appeared in 1917. In 1920, in Detroit, another police officer named William Potts introduced a third, yellow light. Two years later, automatic timers were introduced to traffic lights, doing away with the need for policemen to be present.

Inspired by their New World cousins, European nations soon followed suit. The first traffic light in Europe was installed in Paris in 1923. Berlin was next in December 1924. London did not see its first electric traffic light until 1925, some 57 years after its first disastrous experiment with the idea.

Rules only work if everyone knows what they are, and in the early days of traffic lights there was a great deal of confusion over what the different colours meant. In the US, some sets of lights used green, yellow and red lights; while others used green, white and red. As late as 1924, drivers routinely got mixed up as to their meanings. ‘Our system provides an orange signal for go’, claimed one New York citizen in 1924 and ‘a green signal really for stop…’

The order of lights also created a problem. Sometimes the green light was on the top of the three, other times it was at the bottom. In Syracuse, New York, the Irish-American population insisted that the green light should be at the top, because green was the colour of Ireland and should naturally stand above the red colour of its British oppressors. It wasn’t until after 1924 that a standard sequence was agreed – red at the top and green at the bottom – and the ten per cent of male drivers who were colour blind could finally breath a sigh of relief. This decision was made at the first National Conference on Street and Highway Safety, chaired by future US president Herbert Hoover.

Meanwhile, the League of Nations also got involved. At a conference in Geneva in 1931, a whole host of standardised street signs were discussed, including the universal adoption of red and green traffic lights to signify ‘stop’ and ‘go’. As in America, it was agreed that in vertical sets of lights, the red light should always be at the top and the green light at the bottom. The international rules on road signals were finally codified and globalised after 1968 at another international convention in Vienna.

What nobody thought to clarify is what exactly is meant by the word ‘green’. This has become a particular issue in Japan, where the traffic lights are actually blue.

When the first traffic light was set up in Tokyo in 1930 it was an imported model from America, with a light just as green as anything seen in the Irish communities of New York. But the word that everyone used to describe the ‘go’ light was 青 (Ao) – a word that originally could mean either ‘green’ or ‘blue’ (it actually referred to a turquoise-like colour that was somewhere in between). Nowadays, in virtually every other context, this word is always translated as ‘blue’.

In 1973 the Japanese government decided that calling a green light ‘blue’ was simply too confusing. So they decreed that all green traffic lights should be changed to the bluest possible hue while still staying within the international rules. As a consequence, Japanese traffic lights today are a completely different colour to any other traffic lights in the world. 

The traffic lights of today have come a long way from the mechanical, gas-powered device used in London almost 160 years ago. Their sequencing has become increasingly computerised since the 1950s to allow for better traffic-flow not only at individual junctions but across whole cities. Pressure plates and magnetic induction loops have been placed within the asphalt of the road to measure how much traffic is passing through a particular junction, so that busier routes can be given priority. Some traffic lights have audio detection so that when they hear an approaching police or ambulance siren they can override the normal light sequencing, switch the lights on all side roads to red, and allow the emergency vehicle through.

Today we are on the brink of an era of artificial intelligence. Experiments are already being conducted by companies and universities whereby computers can observe the movements of all road users, including pedestrians, with high resolution cameras and radar sensors. They can then make their own decisions about how best to maximise the flow, and safety, of each. Meanwhile, Google has launched a system called ‘Green Light’, whereby traffic data from Google Maps is used to maximise the sequencing of traffic lights in whole cities. The system is already being used in Seattle, Hamburg, Manchester, Rio de Janeiro and many other cities around the world.

The logical conclusion of this march of technology is a world where driverless cars communicate seamlessly with traffic-control systems, and arrange travel without any human input at all. In such a world, who knows if traffic lights will be needed? Perhaps the day is coming when streets will once again be free of these machines, just as they were in 1868.