How about the detection units? I am considering getting some very small capitive proximity switches and mounting them up through the benchwork through the ties.
What about the logic circuits? Simply whichever proximity triggers first lowers the gates, and the second one triggered raises the gates?
I found some operating gates at the LHS for $39 a pair. I will need to build a flasher and use a tortoise to raise/lower them.
I'm thinking I want to scratchbuild the circuits/operating mechanisms.