barriers and surfaces

so i figured out how to build roads in the game you just have to utilize barriers (they should unlock very early after concrete production) i would like to see the use of dirt and gravel as a defined surface that say -5% maint for dirt (will be fairly obvious as no grass grows) and -10% for gravel (give a slight yellow tint to placed gravel surface) when placed as an improved surface

Do you have update 2? It has pretty much exactly this. A variety of concrete based surfaces, paint decals for road markings and such like, and they give a maintenance reduction for vehicles on them.