A trailer-mounted crash impact attenuator is disclosed for attachment to a host vehicle, which comprises an anti-rotational attachment system having an internal support tube and a plurality of external support tubes. The internal support tube has a connector on its front end for attachment to a suitable receptacle on the host vehicle, and the plurality of external support tubes each have an anti-rotation support pad on a their front ends. At least one of the internal support tube and the plurality of external support tubes is comprised of a telescoping construction. A backup frame is disposed on a rear end of the attachment system, and a crash attenuator unit is disposed on an axle and pair of wheels for mobility. When the crash attenuator is impacted by an errant vehicle, the anti-rotational attachment system is actuated to prevent the trailer mounted crash impact attenuator from rotating relative to the host vehicle.