The eccentric engineer

E&T turns left at the robots and proceeds to discover the fascinating history of traffic lights.

Those of you who haven't been to South Africa might be alarmed at the idea of turning left at the robots. The image conjured is an uneasy one - of street corners inhabited by listless mechanical men brimming with technology but with so little purpose that they can be used as landmarks when giving directions. Of course, South African robots are not mechanoids but simply the local term for traffic lights, which came as something of a disappointment to me, I must admit. Not that the invention of the traffic light should be dealt with too, er, lightly.

The origin of the traffic light is a splendid story of great British inventiveness followed rather rapidly by a sudden and somewhat explosive reverse. The first true traffic light was produced, rather counter-intuitively, before there were any cars on the road. The man responsible was John Peake Knight, a railway engineer, who specialised in designing signalling systems for the burgeoning railways. The signals of his day consisted of a semaphore arm which was either in the horizontal position or at 30 degrees to indicate whether a train could pass during the day. The semaphore arm also obscured or revealed either a green or red lamp, depending on its position, to indicate whether the track was clear to pass at night or when the arm itself might not be fully visible.

The problem that the good burghers of Westminster faced in 1868, however, had nothing to do with trains. It was the huge increase in horse-drawn traffic streaming over Westminster Bridge and the effect it was having on thousands of pedestrians thronging the precincts of the Houses of Parliament. So JP Knight was approached to find a solution, which he duly did, installing the very first traffic lights at the intersection of Great George Street and Bridge Street on 10 December that year.

Not surprisingly, his system was effectively the same as a railway one. At its centre was a semaphore arm and a revolving gas lantern with a red and green light which could be operated by a policeman to stop the road traffic to allow pedestrians to cross. The system was a triumph, hailed by everyone, except the poor policeman who had to stand next to it all day. In fact, just under a month later, the policeman on duty had even more cause to rue his luck when, in mid-operation, the whole device exploded, injuring him.

And that was the end of the traffic light. Well, not quite. Move the story on another 40 or so years and across the Atlantic where engineers were again thinking about the knotty problem of traffic control. Cars had been introduced in the US in the late 1890s and their relatively high speeds and unfortunate conjunctions with horses, people and occasionally each other meant some form of prioritising was necessary.

Perhaps, the first man to think about what this should actually be was Earnest Sirrine of Chicago who filed a patent in 1910 for what he claimed was "the world's first automated stop-go system using non-illuminated boards, with the words 'Stop' and 'Proceed' written on them".

This was all well and good but the lack of lighting meant that its use was somewhat limited. Fortunately, another invention was galloping to the rescue.

Electricity grids were spreading across US cities, and electric light looked like the perfect, non-explosive way to ensure the stop and go signs were always seen. Or so thought Lester Wire, a policeman from Salt Lake City, who set up the first electric red/green traffic light system there in 1912. Sadly, Wire forgot to patent his device, something that James Hoge did not forget to do the very next year. His lights were installed in Cleveland Ohio in 1914 and added the novel feature of a buzzer to help those who had either nodded off at the lights or, through colour-blindess (or simple blindness), couldn't see the colour. 

Which brings the story to its final dénouement. The problem was that these systems consisted of just two lights. As red-green colour-blindness is relatively common (affecting 7- 10 per cent of men), this was problematic, as was the fact that sudden light changes were hard to react to quickly enough - particularly as traffic speeds increased.

The answer came from another policeman - officer William Potts of Detroit. Potts was concerned about the almost impossible task of coordinating policemen on a four-way junction to change their lights at the same time. The answer he found was so simple and effective that it is, fundamentally, the same that we use today. Potts added an amber light (as he had seen on the railroad) and also a timer to co-ordinate a four-way set of lights, cobbled together from a $37 flashing unit used for illuminated signs.

In October 1920, the world's first fully-automatic three-light electrical traffic light system was installed at the intersection of Woodward and Michigan Avenues in Detroit. Potts, like his police colleague Wire, never patented his device, perhaps thinking it was just a public service, and it was left to the traffic light manufacturers to fight it out in court over who should profit from his discovery.

He died in obscurity, unrecognised outside his home city. But you can still find officer Potts' robot standing duty at intersections around the world.

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