<P> 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 . </P> <P> 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 . </P> <P> 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 . </P> <P> Numerous accidents would have been prevented by the provision of track circuits, including: </P>

Which device would best aid in short track detection