ATLS Crossing Troubles: ATLS behaves differently for different trains


Active member
There is a particular grade crossing on my layout that works normal when tested with just a single loco.

When the same crossing is tested with a longer Santa Fe Superchief passenger train with a pair of f7 units on either end of the train, the crossing acts goofy.

As soon as the train passes the gates go back up again. Good.

The bad. About 5-10 seconds later, the gates come down again for about 5-10 seconds then go back up again.

What's up with this?

I am using the 4-trigger, two way mode.

The train approaches the crossing then goes through a junction, diverging tracks following the crossing.

The final trigger the train runs over is beyond the switch points.

Still a single locomotive with no other train cars works normally.

Does having end helper engines on trains create special problems for ATLS?

Is ATLS sensitive to the makeup or size of a consist?

Should ATLS track triggers NOT have a switch in between them?
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Junctions should not make any difference unless a train passes the first triggers and goes on the diverge with no triggers. All trains must pass 4 triggers each set to 4 trigger mode. Don't place a trigger to near the junction because if the junction changes it can see the train several times causing the ATLS to be out of sync.
Length of train should not matter, nor should the addition of locos anywhere in the consist. Is there another nearby crossing with triggers on the wrong channel? As far as a junctions are concerned, as long as a train runs the correct number of triggers, there should be normal operation of a crossing. I would recommend putting a trigger on each diverge of the junction so any train hits 4 trigs no matter which way it turns. I cannot think of a reason why a single loco works fine while the full train acts goofy. I'm thinking the issue is in the trigger settings or the slaves.
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