Heres the way I do it.
I used the free trailer plugin from dstorm to animate a thin segmented ribbon of polys along the path of a null object. The ribbon follows the path and deforms to it.
2. Once the ribbon object is animated mdscan it using clothfx to scan motion of the mdscan plugin.
3. Hardlink the roller coaster to the ribbon object. Heres the result: http://www.3dtrainingonline.com/examples/roller_coaster.mov
In modeler I used the same spline to:
rail extrude the tracks
rail clone the ties
create a motion path for the null in layout.
Thanks Splinegod. I like the way you did that, but I'm helping a friend that made a lot of bones in 9.6 to bend a highway around a sphere and he doesn't want to bend them again. Funny thing is that I exported this scene from 9.6 as 9.2 and imported it in 9.3.1 and the moment it loads it works as it should. He'll try to do that too. Thanks for the help!!