Glad you mentioned this, it reminded me that I spoke to Cale about this. They use a white mindstorms “intelligent brick” (NXT) to alternate the trolleys by powering the track for different time intervals. The NXT also controls a motor which mechanically changes the switch track inside a building near the track.
The task of the NXT is to
1. power the track for 10 seconds so one trolley runs to the other end
2. turn the track power off for a certain amount time
3. reenergize the track, but reverse the track polarity for 10 seconds so the trolley returns to the shed
4. turn the track power off
5. energize the motor to through the switch
(only the side of the switch that is lined up will become energized)
6. reenergize the track so the other trolley leaves
With regards to running trains for weeks on end at a Christmas display, without supervision, (think PPG plaza,) their solution was to have a push button which powers the train for so many loops then shuts off. The train only runs for a short time when someone asks it to run.
Pennlug setting the bar again at brickfair. automated switches with NXT.
Running trolleys today on the PennLUG layout at BrickFair Virginia.
Posted by Brick Model Railroader on Sunday, August 6, 2017