Railroad crossing gate lights. The closed switch represents a train on the track. The closed switch shunts the input of the transistor causing it to switch off which switches off the relays. The transistor and relays going off turn the flashers on. It's a FAIL SAFE circuit in case the transistor or relay fails the lights go on so no one will be on the track when the train comes. Also in case the clock pulse fails 2 of the LEDs will come on and stay continuously lit while the train passes. The green graph indicates that there is only 857 mV across the track, and the blue graph indicates 500 uA thru the track when a train passes so it's safe to touch the rail
