Crossing signals

[Anonymous]

I was just wondering how grade crossing signals work. Some kind of gap in the rails or wiring in the rails?

Matt

[thirdrail1]

The steel wheels and axles complete the circuit. The rails are isolated with insulated rail joiners, which are only evident on close inspection.

[wabash1]

at the start of the circut is a device called a starter. it is for lack of better words like a radio frequancy. the frequancy of the starter is matched to a card at the crossing. when the train shunts the track on the newer crossing it takes a reading on how fast the train is moving and activates the crossing lights for a 15 sec advace warning. when the train is 5 ft(give or take ) from the crossing it gets on a circut that is called the island. this circut runs thru the crossing to 5 ft past at anythime a car is on this circut the lights will not time out. the time out will work only if the train is not on the crossing. this is how they can tell what crossing is down and why. in towns that have crossing close together as not to have all signals come on at same time if you have six crossing and a switcher is blocking 2 why have the last four come on if not going to be used holding up traffic.

[Anonymous]

How long does it take for the signals to time out if the island circuit is not completed?

[wabash1]

it should be 30 secs some are quicker and some slower. that is if the train is stopped or moving real slow. otherwise it wont time out.