Grader

To grade a road, the grader makes 3 passes.  The first pass pushes the shoulder material from one side onto the centre of the road.  The grader returns on the opposite side and does the same.  The final pass is down the centre of the road to flatten the surface.
     This way, the shoulder is cut down and the crown established.  Thus water is not held in the tracks made by vehicles.  At least this is the theory.