exploded view of the mechanism of detachment guard rail beam 17 is normally attached to support post 18 by means of a bolt 19 in accordance with the invention the bolt 19 passes through a tapered aperture 40 within reinforcement 20 and is securely affixed to post 18 thus bolt 19 passes through a hole 42 in the post 18 bolt 19 is fitted with a reinforcing sleeve or 34 bangee 34 21 which provides space between the beam 17 and the support post 18 and also protects the shaft of bolt 19 from lateral impacts when a vehicle strikes the end piece the base members 11 of the end piece travel along the guard rail beam 17 until they encounter the reinforcement 20 at this point the 34 bangor 34 14 impacts 34 bangee 34 21 thereby moving bolt 19 along the widening aperture in reinforcement 20 as bolt 19 is pushed from the narrow end toward the wide end of the aperture 40 the aperture becomes sufficiently large to enable the head of bolt 19 to escape from the aperture upon such disengagement of the bolt 19 from reinforcement 20 the guard rail beam 17 is released from post 18 this type of disengagement of course may occur at more than one post.