i can see this as a very nice christmas tree diorama addition. in n-scale. the whole tree stand maybe in the box - anyway

 

Well that is interesting!

 

This is a similar to a project I have been trying to find an answer ti for a couple of years now.

The problems are 1, I am doing this in 0 Scale ,2 my roads are not flat pavement but ,a1920's gravel road, that moves up and down with the terrane, 3 my vehicles weigh a few oz. instead of grams. finely 4,the mechanism needs fit in the structure of the hwy. bridge.