Convert the landscape to a grid (mesh) of rolling curves, then use network to make a rolling surface.
Flow the roads, using their plane, onto the rolling surface.

- Brian

So making the mesh is the question.
For points with a given x value, make an interp curve.
For points with a given y value, make an interp curve.

Assuming x values, and y values are index-able, write script with outer FOR loop for x = i, inner FOR loop for y = j, to make the computer screen vertical interp curves.
Increment the indexes with the grid interval.

Repeat with y = i, x = j , to make left to right interp curves.

The lineweb script could be re written...