reinforcing rib 41 this effective thickness of course represents the static condition of the structure of the delineator on impact bending forces cause the contortion of the outer ridges 43 in angular rearward movement this structural deformation facilitates improved bending because of the concurrent reduction of apparent thickness of the delineator body and moment of inertia such structure directly implements the concept of variable ei product in response to static and dynamic conditions in fig5 the deformed delineator 50 is shown immediately after impact with an automobile 58 the elastic forces of the delineator are in the process of restoring the upper portion 59 of the delineator to its original upright position fig6 b illustrates the unflexed apparent thickness of the delineator viewed at the cross section view taken along line 6b here the hard ground structure forces the delineator to retain its static configuration having an apparent thickness extending from i to iv it is this extended thickness d t which strengthens longitudinal rigidity in the otherwise thinned web structure between ii and iii and provides the higher ei for this condition such configuration is modified however during contortions illustrated in fig5 as represented in the fig6 a view the thinner structure of the web body 62 permits greater flexibility and causes rotation of the more massive ridge members 63 in angular rotation rearward the effect of such contortion is to reduce the thickness of the delineator from its static thickness of d t in fig6 b to a reduced thickness d i of fig6 a the relationship defined by equation 2 shows that any reduction in.