Abstract: The vehicle frame has a rear section carrying the engine and passenger bearing cab, and a front section carrying a resiliently mounted bumper. The two frame sections have confronting, overlapping end portions connected together for pivotal movement relative to each other about a vertical axis. A releasable locking pin is normally retained by a frangible detent in an operative position in which it prevents any pivotal movement of one frame section relative to the other. When the bumper collides with another vehicle, or the like, it drives a release pin against the locking pin thereby breaking the detent and releasing the locking pin while simultaneously causing the front frame section to be swung out of alignment with the rear frame section.