PLEASE READ CAREFULLY!
I understand and I hope I can help other people understand too. So, I did a crossing test today with the ATLS system with an SD40-2 and 3 cars behind it. So, the ATLS 4 and 2 trigger system require 2 or 4 triggers to be activated and deactivated by a train to activate crossings or other trackside accessories. That doesn't mean you actually need 2 or more triggers, you actually could have 1! However, you would have to activate and deactivate it twice with a train. Putting 2 triggers close to the crossing is actually a good idea because both of them are activated at the same time which means when the train exits the crossing area, it will deactivate immediately. With the triggers farther away, switching becomes an issue. A train long enough to activate 2 or more triggers far apart from each other is a very easy situation for you not to mess up the crossing. However, as your train gets shorter as you switch cars, the train doesn't reach both triggers. This ISN'T a problem if you are only going one direction with the triggers far apart. It IS A PROBLEM when you stop the train in the middle of the crossing when you have only activated one of the triggers and then start to reverse. This causes the crossing to stay on because you didn't activate and deactivate the 2nd one so the crossing would turn off. For now, to fix the crossings, all you have to do is pull a train up to ONE of the triggers activate it and deactivate it. This will deactivate the crossing allowing traffic to flow again.
I have already proposed that the ATLS Slave have a off and on button to turn the invisible train on and off. I think this would work perfectly so we could just quickly turn the crossing off with a few clicks of the mouse.