Track Circuit - History

History

The first use of track circuiting was by William Robert Sykes on a short stretch of track of the London Chatham and Dover Railway at Brixton in 1864. The failsafe track circuit was invented in 1872 by William Robinson, an American electrical and mechnical engineer. His introduction of a trustworthy method of block occupancy detection was key to the development of the automatic signalling systems now in nearly universal use.

The first railway signals were manually operated by signal tenders or station agents. When to change the signal aspect was often left to the judgement of the operator. Human error or inattentiveness occasionally resulted in improper signalling and train collisions.

The introduction of the telegraph during the mid-nineteenth century showed that information could be electrically conveyed over considerable distance, spurring the investigation into methods of electrically controlling railway signals. Although several systems were developed prior to Robinson's, none could automatically respond to train movements.

Robinson first demonstrated a fully automatic railway signalling system in model form in 1870. A full-sized version was subsequently installed on the Philadelphia and Erie Railroad at Ludlow, Pennsylvania (aka Kinzua, PA), where it proved to be practical. His design consisted of electrically operated discs located atop small trackside signal huts, and was based on an open track circuit. When no train was within the block no power was applied to the signal, indicating a clear track.

An inherent weakness of this arrangement was that it could fail in an unsafe state. For example, a broken wire in the track circuit would falsely indicate that no train was in the block, even if one was. Recognizing this, Robinson devised the closed loop track circuit described above, and in 1872, installed it in place of the previous circuit. The result was a fully automatic, failsafe signalling system that was the prototype for subsequent development.

Although a pioneer in the use of signals controlling trains, the UK was slow to adopt Robinson's design. At the time, many carriages on UK railways had wooden axles and/or wheels with wooden hubs, making them incompatible with track circuits.