A system used to detect and annunciate a loss of occupancy detection in transit systems normally operating under automatic train control operation is disclosed. Upon manual or automatic engagement of operation the system, in collaboration with the existing automatic train control electronics, detects and annunciates the loss of occupancy detection by querying the train's trailing speed control blocks for any valid nonzero speed command that would allow other trains to enter that already occupied block—causing a collision! Additionally, in the present invention the system's self checking error and failure detection operation is automatically checked during normal running mode of operation and as such each individual component of the entire automatic train operation is checked for failure in its entirety and the system is void of undetected latent failures owing to its design, stability, and simplicity of operation.