I recently did a project with some simple topo needed in a track/road like situation. Although not quite as complex as your roads, it may be worth a look. (Kindof hard to see but the go Kart track is going up and down and banking in the corners and such)



Really if all you need are some subtle changes for a couple areas, especially with roads that can be defined, Maybe just make a grid surface that you can trim the roads out of, then lower and blend them. The grid surface can be raised and lowered in some key areas with point pulling to create some levels.

2 cents.