Thanks for the info. good comments. Just to clarify the reasons that I want the train to slow down slowly rather then an abrupt stop is that it causes wear on the gears and can derail the following cars. Humm from the comments I am thinking that perhaps what I need to do is to cut one of the wires to the throttle on the power pack and have this wired into a relay. When someone walks into the display the motion detector turns the power on that turns the relay on which closes the contact and completes the power to the throttle thus with the momentum switch turned on the power to the track slowly comes up and the train starts slowly. When the motion detector times out the power turns off to the relay that then cuts the power to the throttle with the power pack still on this will allow the power pack to slowly turn the power down to the track.
Using a larger flywheel in the engine is a good idea but I am using small simple Lionel engines. I am hoping to find an electronic solution.
Here is an article on using capacitors a friend sent me that was very informative!
