Impact protection structures for vehicles are described. An impact protection structure includes a support structure of the vehicle, an interior rail coupled to the support structure, and an exterior rail coupled to the interior rail. The exterior rail has an inboard boundary wall positioned between an upper mounting region and a lower mounting region. The upper and the lower exterior mounting region of the exterior rail are coupled to an upper and a lower mounting region of the interior rail. At least a portion of the inboard boundary wall is spaced apart from an outboard wall of the interior rail such that when the exterior rail is impacted by a blunt-object barrier, the inboard boundary wall of the exterior rail deforms, thereby damping energy of the impact at the exterior rail and arresting crack propagation between the exterior rail and the interior rail.