The first pedestrian crossing signal was erected in Bridge Street, Westminster, London, in December 1868. It was the idea of John Peake Knight, a railway engineer, who thought that it would provide a means to safely allow pedestrians to cross this busy thoroughfare. The signal consisted of a semaphore arm (manufactured by Saxby and Farmer, who were railway signaling makers), which was raised and lowered manually by a police constable who would rotate a handle on the side of the pole. The semaphore arms were augmented by gas illuminated lights at the top (green and red) to increase visibility of the signal at night. However, in January 1869, the gas used to illuminate the lights at the top leaked and caused an explosion, injuring the police operator. No further work was done on signalled pedestrian crossings until fifty years later.