Abstract: A crash attenuator for protecting a truck or stationary structure from damage resulting from impact of an object such as a vehicle including a fame mountable to a truck or stationary structure, a bumper having an impact-receiving face adapted to receive an impact from an object in a crash, a movable displacement structure coupled to the frame and interposed between the frame and the bumper and having a first position in which the bumper is relatively distant from the frame and a second position in which the bumper is relatively proximate to the frame, and an energy dissipation system coupled to the displacement structure for dissipating the impact energy of the object into the bumper which causes the displacement structure to be moved from the first position toward the second position.