I had some black tape I used to use for printed circuit board layout. It comes in widths ranging from .010 in. to .5 in. I used .040 in. for N scale and put it on some acatate, then painted it with several coats of acrylic paint. When it is pulled of of the acatate, some of the paint kinda flakes off if the tape streches, which is great since it gives a worn look when put on a black "asphalt" road.
You should be able to find this tape at a drafting supply store. I'm not sure, but I think Chartpak is the only company that still makes this tape, thanks to computer PCB design layout programs.
Don