Image credits:
Broken asphalt:
http://commons.wikimedia.org/wiki/File:Deteriorated_asphalt.jpg
Gravel, pebbles:
http://commons.wikimedia.org/wiki/File:Indiana-rural-road-dirt.jpg
Insect impact:
http://commons.wikimedia.org/wiki/File:Insekt%2BStreichholz.jpg
Winter salt:
http://commons.wikimedia.org/wiki/File:Sal_%28close%29.jpg
Sand, Dust:
http://commons.wikimedia.org/wiki/File:SandRoad.jpg
Fresh paint:
http://upload.wikimedia.org/wikipedia/commons/2/2d/Safe_Road_Construction.jpg
Debris:
http://commons.wikimedia.org/wiki/File:Littering_in_Stockholm.jpg