An interlock circuit is adapted to be activated by the first sensor to prevent a change in the signal light output until {HEAD ~ the third sensor} at the crossing is triggered by {TAIL ~ the passing} of the first vehicle through the crossing releasing the interlock circuit 
An interlock circuit is adapted to be activated by the first sensor to prevent a change in the signal light output until { HEAD ~ the third sensor } at the crossing is triggered by { TAIL ~ the passing } of the first vehicle through the crossing releasing the interlock circuit
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH