Ok so what makes the crossing lights/gates work when a train is coming?

Question

What actually makes them come on? I figure it's electrical but what tells them to come on ... is it something on the tracks?

Answer 1

There is a trip sensor when the train goes over the track. Then it sends a signal to the electric box and the lights go on and the big gate goes down.

Answer 2

sensors and track circuits in advance of the arrival at the grade crossing.

Answer 3

i think theres a trip thing that the train goes over to set them off

Answer 4

Not really a sensor, the wheels complete an electrical circuit in the operation system circuit.. If like turning on a light switch.

Answer 5

There are actually two sensors that activate when the pressure of the rail goes down and they are located 200 yards prior to any crossing.

Answer 6

It's a sensor on the tracks that when the train goes over it, it sends a signal to the lights on the gates so that they can go down.

Answer 7

There are sensors in a track. They feel the many tons of trains coming around. They don't always come down at same time, as they maybe going faster.. But a sensor

Answer 8

They are activated when the trains steel wheel and axle makes a complete circuit between the two rails. I've forgotten now, but it is very low voltage, like 6 volts maybe?

The stretch of track surrounding the crossing is insulated. In advance (sometimes a few feet, sometimes a mile) of the crossing you'll see where the block starts, as you'll see a yellow insulating H-shaped piece that looks like a bar from the side along side the rail, with a middle that is between the rails. Next to that you'll see a wire welded to the rail. Down the line next to the crossing is a control box that has all sorts of circuitry.

There are more advanced circuits, that when the train enters the insulated block will calculate the speed of the train, and determine how long until the lights come on and gates should go down. This is very handy when you have fast 70mph passenger trains and slow 40mph freight trains on the same track. To keep traffic moving, the crossing will activate early with the faster train, but delay a few seconds until the slower train is closer.

The circuits can also determine if a train stops and de-activate an active crossing. Sometimes the train will have to stop just a few yards short (sometimes more) of a crossing, and it will be activated. There is a circuit that will sense the train has stopped and automatically open the crossing to traffic, then re-activate when the train starts moving again.

Answer 9

Well, there are two wires, one connected to each track, that then connects to the signal and a battery... keeping a very low current going thru all the time, when the train gets to that point, it cancels out the current causing the signal to activate until the train moves out of that circuit and the current from the battery can resume.

Heres a really cool web site that gives diagrams to all the components of signals and so forth.. I found it very informative.