THE FIRST traffic signal was invented by J P Knight, a railway signalling engineer. It was installed outside the Houses of Parliament in 1868 and looked like any railway signal of the time, with waving semaphore arms and red-green lamps, operated by gas, for night use. Unfortunately it exploded, killing a policeman. The accident discouraged further development until the era of the internal combustion engine. Modern traffic lights are an American invention. Red-green systems were installed in Cleveland in 1914. Three-colour signals, operated manually from a tower in the middle of the street, were installed in New York in 1918.