I wired up my displays for the holidays with a motion detector light sensor.
Wired instead of to a light for outside it is wired to a plug.
I cover up the light sensor and it just detects motion and turns on the power for the time you set it to run for perhaps a couple of minutes.
The trains I took out the e-units engines with DC motors.
I used an old DC power pack with momentum from MRC. Tech 3 model 9600
Set the speed for what I want and set the Momentum switch on.
When people walk by the motion detector turns on the power the lights on the layout come on right away. The power slowly increases on the power pack so the engine as a smooth slow start and does not wear the motor and gears out with a fast start.
The flywheel slowly slows down the train when the timer times out and the power is cut.
This works very well for automatic activation without having to add a button and gentle starts for the train.
Willams engines are very reliable for regular runners and keep anything away from track that can get caught up.
I have run the Lionel Polar express this way by removing the e-unit just wiring it direct to power pickups for DC power from transformer.
Note the gears wear out quickly on the Lionel model Williams are more reliable.
Perhaps put a plastic clear sheet up to prevent kids from throwing things on the track.
My layout ran for a few years 12 hour days 7 days a week a month at Christmas season.
Also if using the Polar Express train from Lionel I added some snow mix with silver glitter it dries hard white, can get from Michaels.
I added the Hobo car, glued it in place so will not turn over with the snow around and drilled out the fake fire and added some candy clear foil orange with orange and red flashing led bulbs for a fire.
http://www.modeltrainsoftware.com/bl-213-f.html
Also for the end car I drilled it out and added a bigger red glowing light as in the movie.
Can add the LED bright headlights as well.