Ideas on how to do something...

[Jagdrive]

If you are using it as the travel from the ground to overpass, might i suggest a rack-and-pinion style of track. I think a decent size motor would be able to handle the demand of the ball directly. But, if you think the motor can't, then worm gear will be about the only option with the motor on the fork. Bear in mind that the travel will be really slow with the high gear ratio.