My idea was to invest in the Kato switches that activate their crossing gates. Set it up so the bridge is up in the natural position, and when a train hits the sensor, it drops into position. Would probably need three doubles, maybe more, to pull it off. But definitely a "dead zone" would be necessary.
If operators could be disciplined enough to approach the bridge at a lower speed, it could be a really cool feature to add to a set up.
Lee