An aerodynamic structure attached to the sides and top of a truck cargo body (either a stand-alone trailer or a “straight truck” with the cab and cargo area as a fixed vehicle) at the aftmost region, which rear typically contains a rolling door assembly, which rolls upwardly. An aerodynamic structure is permanently attached to the sides and top of the trailer in a manner that extend past the aftmost plane of the truck cargo body and retract to the aftmost plane of the truck cargo body when subjected to a force, allowing this device to be backed into structures. The retracted orientation allows for the rear of the trailer to be fully accessible for loading and unloading, and does not reduce the size of the opening of the trailer. The various embodiments of the invention allow for automated deployment once the force used to compress the structure is removed.