There are three main circuits that a railroad crossing uses. There's the two approach circuits on either side, and the island circuit which is the actual crossing itself. Some signal circuits are equipped with timers that will make sure the train has absolutely stopped in the approach circuit and not the island circuit, and time out the signals.
Crossing gates work by a simple relay block in the relay case (where the electrical components are.) that have a timer in them and send a signal for the gate mechanism to bring the gates down and close the road. When the train has left the island circuit and cleared the approach block it came from, the gates will rise and the road will reopen. Crossing bells work the same way with a signal being sent to them.
* Added - The track circuits that activate the crossing systems when a train approaches do not rely on the train "completing" a circuit, as this type of circuit is illegal in the US and many countries. The train either "shunts" the circuit or in the case of electronic circuits, the electronics sense the train, which can include sensing its speed.
railroad crossing signs are railroad crossing signs, a baby could figure that one out.
An X. Because it is a cross for the railroad crossing.
The purpose of a railroad crossing sign, is to let you know that there is a railroad coming up or that there is one right in front of you.
The Transcontinental Railroad
Be happy and think then you will get the answer
level crossing = railroad crossing
An uncontrolled railroad crossing warning sign is typically yellow with a black symbol. The sign features a graphic of a railroad crossing and may include the words "RAILROAD CROSSING." This color combination is used to alert drivers to the potential danger of an approaching train without any control measures in place.
Railroad crossing
railroad crossing sign
On average there are 430 people that dies due to railroad crossing each year. There are approximately 4,900 people that are injured at railroad crossing as well.
Railroad crossing signs are either a white x shape with the words railroad crossing inside of them or a yellow circle with a black x and the letter R on the left and right side.
When within 100 feet (about five car lengths) of or crossing an intersection or railroad crossing.