for movement longitudinally of the rails the cross rods serve as supports for transverse impact walls 14 15 and 16 generally upstanding and at their ends carrying pairs of side walls 17 18 and 19 these are disposed opposite each other with respect to the center line and preferably are somewhat overlapped these side walls are preferably made of horizontally corrugated stock and thus interfit and partially overlap to aid in guiding each other for movement toward and away from the abutment 7 the leading impact wall 14 has a forward extension providing a nose piece 21 this is preferably of some sort of absorbent or accommodating material so that a vehicle for example impacting against the nose piece has some cushioning the normal spacing of the impact walls 14 15 and 16 from each other and from the abutment 7 is provided in part by a housing 22 of conveniently rectangular form disposed immediately in advance of the abutment 7 and serving as a mounting for a number of spring bundles 23 each spring bundle preferably includes a pair of plates 24 and 26 having a number of spring cups 27 embossed therein the cups serve as positioners and mounts for intervening coil springs 28 29 30 and 31 the springs in the normal released condition are given a slight initial compression and are prevented from expanding unduly by a central tie 32 passing through each adjacent pair of cups and serving as a limit stop therefor conveniently the number of springs varies with the design characteristics and performance.