Railroad highway crossing warning system

A railroad highway crossing warning system comprising, means for sensing current flowing in the track rails of an approach zone, means for sensing the voltage across the track rails, means connected to said current and voltage sensing means for filtering the voltage and current derived from the track rails, means connected to said filtering means for calculating the track impedance, means connected to said filtering means for detecting the phase angle between the voltage and current, means connected to said impedance and phase angle means for linearizing the calculated track impedance by multiplying the track impedance by a function of the phase angle, means connected to said voltage filtering means for detecting coded signals in the track rails, means connected to said linearizing and coded detecting means for sampling the linearized track impedance at given periodic intervals, means connected to said sampling means for detecting the motion of a train and for predicting the time of arrival at the crossing by comparing the predicted time of arrival at the crossing with an advance warning time, and means connected to said motion detecting and predicting means for activating the warning apparatus at the crossing when the predicted time of arrival is less than the advance warning time.