The first traffic lights in the U.K were installed by J.P. Knight outside the Houses of Parliament on December 10, 1868.
J.P. Knight was a railway engineer. The lights, patterned after railway signals, had semaphore arms with red and green gas lamps to signal stop and go.
The number of traffic lights in the U.K. has grown significantly since 1868. Now there are approximately half a million traffic lights in the U.K. now. This is in addition to the many roundabouts.