Gas-lit traffic signal, 1868.

Drawing showing the first street crosing lights which were erected outside the Houses of Parliament, London in December 1868. The lights, which gave red or green 'stop' or 'go' signs to traffic in each direction, required a policeman to operated them. The traffic signal lights were invented by Saxby who also worked on railway signals. The project to install these traffic lights all over London was abandoned when a gas explosion shattered the lights and injured the policeman operating them.