Andy,
I posted some photos of my streets. The streets are made from drywall compound or Plaster of Paris. I started with Plaster of Paris but it gets very hard once cured and is difficult to sand. So most of the street is drywall compound. I build wood forms and trowel in the plaster. Once it is set, I sand it and stain it with a wash of Model Master Sand (4720). Then I use a modeling knife to scribe the joints. Since drywall compound shrinks slightly as it dries, small cracks appear that add to the appearance. I also added some oil stains - I use real oil off the dipstick from my car. I also added faded/worn white stop lines at each RR signal.
