I’ve often noticed that when trains are stopped perhaps a hundred feet or more from a road crossing that the gates remain in the up position. Does the engineer control this and aren’t the gates automatically activated when a train approaches?
the goat
Most gates are triggered by a switch that is positioned a certain distance from the crossing itself. Most trains know were the switch is. They might stop just before the switch that loweres the gate so it will remain up for cars to cross while it is stopped. Once that switch is activated the gates will come down.
Mike
I think what the OP is asking is, with the engine sitting 100 feet from the crossing, where the gates would normally be down, they are up, most likely a crew change spot or close to a yard. I sure the switch you are referring to is a lot farther away from the crossing than 100 feet, so the question again, are the gates and/or signals turned off manually by the crew or dispatcher when the train is idle very close to a grade crossing? (within 100 feet or inside the area where the gates would normally be triggered?)
I knew this answer at one point, but I’m a little foggy on it right now. Real railroads use a system very similar to how we detect trains on our model layouts. The track itself is insulated in pre-determined blocks. There is a low voltage reference between the two rails (3 volts I believe) that is used to trigger the system. The length of these blocks varies with the ruling train speed in the area of the crossing - the active section is considerably longer on a high speed main as opposed to within city limits.
The engineer is able to introduce a shunt resistor into circuit within the locomotive which will de-activate the given crossing he is at. This shunt increases the 3 volts to 12 volts which activates a relay shutting down the initial relay that turns the system on - kind of a two-stage relay. This way, if the train is sitting within the detection block, but will not actually be crossing the grade, he is able to manually release the gates and allow traffic to cross.
If you carefully inspect the area where the detection location is, you can identify it by a half inch thick heavy fibre insulator between two rails. This spacer is cut to the exact same profile as the rail itself. Also, the rail joiners themselves are also insulated and can usually be identified by them either painted white or yellow.
I’m sure with todays technology, this concept is probably becoming old fashioned, but I recall this type of system still in use most recently.
Mark.
The flashers would always be active, the circuit near the gates would always drop the gates, if the train is in the circuit but stops short of this there may be a timer that raises the gates keeping the flashers active. The circuit would detect train direction. Once the train moves it would hit the gates down section and down they go.
Most gates are not triggered by a “switch”, in the physical sense.
Most gates are triggered by a track circuit (which could considered a switch in some ways) that is long enough to cause the gates to be be lowered prior to a train traveling at maximum speed reaching the crossing. Modern gates have speed sensors in the detection circuitry that detect whether a train is moving or stopped, or time out. If the train stops or takes too long, the gates will time out and they will go back up again. When the detector circuit detects the train beginning to move again, it re-actvates the gates and they come back down.
The train may know where the detection circuits start and sit off the detection circuits or they might step on teh circuit and then stop and the gates will go back up.
Mark,
Very interesting!
Thanks, Ed
Good answer. A railroader friend of mine explained the new motion detector technology. I’ve seen it myself, when trains ease up to a crossing, and stop, and the gates go back up. When they begin moving again, they start very slow, so the gates can come back down, before they are on the crossing.