509 Electrical Light Display Block Signal

509 Electrical Light Display Block Signal. Circa 1930. , As railroads developed in the mid-nineteenth century there was a need to control the traffic on the railroads., The first attempt to control traffic was by the use of the telegraph system. Station Masters would have the normal printed schedules and be informed by a telegraph message of any unexpected changes that occurred. It was their job to inform the crew operating the train of these changes. As traffic continued to increase this method became too slow and cumbersome., The next big step was the "Block Tower" system. On the Northern Central Railroad almost all of the towers were hexagonal in shape and two stories high. Each of these towers controlled a "Block" or section of track that was three to five miles in length. The controls in the tower where mechanical and operated the local switches and signals by cables that ran through protective chases or troughs. The switches and signals determined which trains had priority for the main tracks and which had to go on the side tracks. They also had controlled the speeds at which the trains were allowed to operate within that block., In the 1930's electrical control systems, including the 509 electrical light display block signal shown here, began to replace the manually operated signal systems. This allowed for the closure of most of the block towers. As the new system was perfected it greatly improved the efficiency and safety of the railroad. Technology reached the point that the electrical conductivity of the metal rails could be used to determine where trains were on the rail system. By the mid 1950's a single operator was responsible for fifty or more miles of track., All trains today are controlled and tracked by global positioning systems.