A motor grader with crab steer can be used to reopen blocked culverts. If the ditch bottom is solid, put the front wheels in the ditch with the rear frame on the road surface. Shift the circle toward the toe of moldboard (the leading edge). Turn the moldboard square to the mainframe and tip it to nearly two-thirds of its maximum forward tip.
Side shift the moldboard, extending the cutting edge into the ditch at the blocked end of the culvert, being careful not to damage the end of culvert. Set the blade angle to match the shoulder slope.
Move slowly forward to remove the blocking material, then rotate the circle to pull the material up onto the road shoulder. Several short passes may be required to reach the bottom of the culvert.
The moldboard may be able to reach the bottom of shallow ditches without articulating the frame.