I've been trying to figure this out using several different methods and keep butting up against a wall.  What I did here was export a terrain map from Carrara into Photoshop and create a road path using a path and the burn brush.  (This pic here is a much smaller resolution than my original).  Unfortunately, I have Photoshop at work and Carrara at home, so I can't test it out until tonight.  But I'd like some feedback from any in the know.  Does this look like it might work?  I don't want this to be a raised road bed, I'd prefer it to cut into the hillside where needed. I'm still fuzzy on if white is high and black is low...or vice-versa. Thanks for any input you might offer.

Of course, if it does work, texturing it is a whole other animal!