Abstract: A highway crossing warning system includes a motion detector transmitter and receiver respectively coupled to the track rails adjacent the highway crossing for detecting motion of an approaching train. Wrap-around approach sections initiate operation of the highway crossing warning, but once motion is detected, the motion detector can serve to inhibit the highway crossing warning, after a predetermined delay, if motion indication ceases. To increase the effectiveness of the motion detector, the motion detector transmitter impresses a modulated carrier onto the track rails, wherein the modulation is phase locked to the carrier. The receiver, tuned to the carrier frequency, detects the modulation, and then determines from the level of the modulated signal whether or not approaching motion is detected. The transmitter employs solid state circuits switched between saturated and off conditions to prevent circuit component failures from masking approach motion.

Abstract: A control system including apparatus for the transmission of information for the control of vehicles travelling in one direction on a guideway. The guideway is broken down into a plurality of groups of uniquely identified sequential blocks. Each block has at least one vehicle detector for detecting the presence of a vehicle and having an operated condition responsive to vehicle detection. Each block further includes a transmitter for providing, to a vehicle within the block, information concerning the block it is in as well as information regarding the identity of the next downstream occupied or unavailable block. To this end, each block has associated with it a word generator for producing a signal identifying the block; the word generator is coupled to the block transmitter, which transmitter is only enabled when the vehicle detector is in its operated condition.