Try wapping the sand paper around a small eraser. Step back and take a good look. If you don't like what you see add some more dirt, wet it, and glue it down then start over with the sandpaper. If it's looking promising add a bit of gravel down the center of the road and along the edges. Do the same with vegetation and maybe a few scraps of wood, scrap paper or other junk.
Vehicles often leave stains behind where they've leaked oil.
Now you're ready to add a car or two and some people. My first attempts at roads were paved. The results were disappointing. Then I remembered reading about using spackle to model roads. For an asphault road my initial preparation is the same as for a dirt road.