@Frank: it's a simple reflective shader with the right balance of reflectivity and specular roughness.
@Dune: I didn't connect these in TG. That would have been really difficult. Actually I imported the terrain into 3ds max (I had to exaggerate the road's boundary displacement to see it there). In Max I created a spline next to the road and duplicated the pole along this spline. I created another spline and connected two points of the pole, converted it into a mesh and applied a bend modifier. I moved the pivot of this "cable" to the first end of it. So by duplicating it several times I could move the cables easily and rotate it to find the next pole. Of course I had to adjust the length each time.
It's quite hard to explain!
When I was finished I exported the whole array of poles and lines as a single mesh and imported it into TG, tweaked the textures properly and voilá. If the road would go uphill, it would have been more complicated, but possible doing it the same way. But it would be overkill to do that in TG I think.