Tripping crossing Gates

[silicon212]

Again, those outside tracks are likely to be industry leads and as such, are not guarded by the automatic warning system.  At least on UP nee SP, there are stop signs on such tracks, which command the engineer to stop his movement and await the warning lights and gates to fully activate and lower.  Look at the tracks in question and see if there are block isolators on them - these look like standard angle joints used to tie together jointed rail or breaks in the rail, except they will have fiberglass between them and the track as the insulator, with wires attaching the rails before and after the joint.  If the automatic system isn't running on these tracks, the only way the warning system will activate is when the rails on the crossing side of the isolators are shunted - in other words, at least one axle of the movement is over them.

[Willy2]

There is one railroad crossing in Fremont, Nebraska where 7 tracks cross the road. If the train is on any of the center tracks, the gates usually activate about 30 seconds before the train gets to the crossing. However, if the train is on either of the two outside tracks, sometimes the gates don't start going down until the train has already entered the crossing. These two tracks are used mainly for switching and the engineer usually slows way down right before the crossing to make sure nobody is coming. Still, I have to wonder why the gates take so long to activate. Can anyone shed some light on this?

[silicon212]

Most crossings use technology such as a grade crossing predictor, that send basically a radio frequency through the rails in addition to the DC current used to activate the signals.  Using the difference in frequency sent vs. frequency returned by the wheels on the train (similar to how radar works), the computer that runs the crossing can determine where, what direction and how fast the train is moving.  The gates are programmed to activate when the train is 30 seconds away from the crossing, give or take.  There is an area, 50 ft or so either side of the grade crossing that is isolated and given a DC power - if the train enters this, the gates automatically go down, no matter what, and stay down until the last wheelset leaves the DC block.  At this point, the computer sees the train moving away from the crossing and raises the gates and shuts off the gong and lights.

Some industry lead tracks do not have the high-tech predictor and are used only with the DC block, as trains on these leads never exceed 10 mph.  There is usually a STOP sign on either end of the crossing, at the entrance to the crossing, where the block detector is.   The train enters the block detector, stops to allow the crossing gates to go down, and proceeds.

[spikejones52002]

Reading over my post "Heart Jump Start Grade Crossing" and the replys got me thinking.

When a train approches a controlled grade crossing. It trips a detector that lowers the gates and/or flashing lights.

Like in Valpo IN. The engine  was stopped 10 foot from the grade crossing. How does it prevent the gates from initiating?

If initiated, How does the gates get deactivated?

When the train is ready to begin movement. How do the gates activated?

Before everyone jumps on me. I know the engineer will wait until the gates are down and the crossing cleared before signaling and begin movement.