To allow the through-running of L&YR trains, the conductor rail was moved to outside the running rails and the centre rail became the earth return until the 1920s. The first automatic train-stop system was installed on the line, and was electrically operated. An arm on the trackside would be struck by each passing train, activating an electromagnet, resulting in a 'danger' signal being shown until the train had passed through the next station. As a result of automation, the number of manned signal boxes was reduced to two. The line upgraded the signalling from semaphore to a Westinghouse permanent daytime colour-light system in 1921: the first to be installed in Britain. The track also contained automatic braking systems for trains which ran through a red light; the current could be automatically disconnected and air brakes applied.