The denfo guy's asphalt shader is the best shader for asphalt I have ever seen. Its great, really. You could just add new planes for things like the middle line, outer white lines ect. It can be located HERE . Most roads in my area are slightly elevated above the ground and come to sort of a point in the middle (makes the water run off into the ditches at the sides). I think you might want to make it out of a poly square or something with depth. Of course this depends on the level of detail and realism you are looking for, and if you cannot download anything.