How Do Traffic Lights Works

There's nothing more frustrating than sitting at a red light, watching smiling drivers on the other side of the road speed past.

But before you sound your horn and shout at the lights, consider the enormously complex network of roads, lights and junctions in which the single vehicle is just a tiny part.

Traffic light timings calculated using complex computer simulations

In London alone, an average 11 million car and motorcycle journeys take place every day. The city has 6,000 traffic lights controlling the flow and a hi-tech control centre monitoring its success.

It is a far cry from the first traffic signals - which were erected outside the Houses of Parliament in 1868 and which controlled the traffic using semaphore armsAs complex as the traffic network might seem, the technology on which it depends is surprisingly old fashioned.








The basic maths of the system was developed by researchers FV Webster and BM Cobbe in the 1960s and is still used to this day - although refined somewhat by the advent of computer simulations.

The other method is a little more hi-tech.

Coiled under the tarmac at junctions and crossroads across the UK, are loops of cable which act as metal detectors as cars pass over them.

This information is passed to a central computer, which uses complex algorithms to calculate the optimal time each light should spend on each colour, ideally creating a smooth flow of traffic throughout the network.

The computers make small adjustments to the timings of the lights, slowly iterating towards the best possible traffic flow. The most hi-tech development is the use of transmitters in buses, which are tracked by the system so that bus passengers are guided as quickly as possible to their destination with the minimum disruption to other traffic.

And in case you were wondering, some lights have a sensor on the top, with the lights programmed not to change at quiet times unless traffic is spotted - so it sometimes is worth edging carefully forward.