Railway control signal dynamic output interlocking systems

A railway interlocking control system comprising a plurality of traffic control devices operative to alternative settings by steady state control signals, each of said traffic control devices having a potentially unsafe setting to which the device may be normally operated by a respective steady state control signal and wherein an erroneous control signal in the potentially unsafe state is by definition a wrong side failure, electronic or computer-based control signal interlocking means for, in normal operation, periodically switching control signals in a potentially unsafe first state between that first state and a relatively safer second state to produce an alternating control signal, signal restoring means, located between the interlocking means and the traffic control devices, for restoring alternating control signals to steady first state control signals, and steady first state signal detecting means, interposed between the interlocking means and the signal restoring means and responsive to steady state signals in the first state, for diagnosing potential wrong side failures.