The first traffic light was invented by J.P. Knight. His invention had similarities to the railway signals of that time. It had semaphore arms, and green and red lamps for night use. This signal was installed outside the Houses of Parliament in Britain. Unfortunately, after only a short period of time in operation, it blew up and killed a policeman. This accident deterred additional experiments, until the era of the internal combustion engine made traffic control of some sort inevitable.
Modern traffic lights work by the red-amber-green system. In some countries there are subtle variations in the sequence. For example, in certain countries, the green and amber light show at the same time. Basic standardization has alleviated the problem of confusing signs. While travelling in a different country, you will notice that the traffic lights are practically the same as ones you find at home.
In cities the traffic light systems are usually controlled by a central computer which can optimise traffic flow by changing the light's sequence in accordance with traffic sensors buried in the road at the approaches to road junctions.
