3D path constraint

hi all, I'm trying to make a cart roll along a track made up out of 3 paths. two for the rails and one centre path slightly lower then the other two. How do I constrain the cart to the track so it banks exactly according the paths I defined? Animating the banking property along the path is hell and far from precise. Any help is more than welcome.

I found a maxscript that does the banking for you - I think it was from 3dbuzz.com.