Sweep in use with 3D Terrain

[Hulston1982]

I am trying to create a sweep that can run along the surface of a Toposurface and was wondering if anyone knows how this can be done effectively.

I have created a profile of a rail track and have used a sweep along Level 0 to form the shape of the rails, but due to the site toposurface being an imported instance of a 3D survey the rails pass through the toposurface at points making it look wrong withing the render.

I know i could creat various work planes and create little sections of track on the varying planes that are at different heights, but feel this could take ages.

I have attached an image to show how the rails pass through the surface.

Any help would be appreciated.

Alex