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