You could do that manually, but I believe with the AM-1S you can set it up to have crossing gates work automatically. The AM-1S has inputs, which means you could put optic sensors on either side of the crossing that would trigger when a train passes. You can create a program for the AM-1S that would start the crossing lights and sounds as long as the optic sensor is activated. Once the train passes, the sensor is no longer activated, the lights and sounds cease.
On my future layout I plan to have a section fed by an AM-1S that will control 2 crossing gates and 4 switches. It should work out well.
-Kevin