I used black "Darice Foam Sheets" (available from craft stores such as Joann Fabrics) which is available in various thicknesses, cut to size and glued down (I used white glue).
Cracks were made with a sail sewing needle, roads were sprayed lightly with Rustoleum "aged iron". 1/8" car pinstriping was used for the striping. Weather with chalk powders and/or paint washes. Tire tracks can be made with a pencil eraser.