Break-away coupling with enhanced fatigue properties for highway or roadside appurtenances

A break-away coupling has a central axis and a necked-down central region formed by two inverted truncated cones having larger and smaller bases joined at the smaller bases by a narrowed transition region in the form of a catenoid having a radius R and a central plane of symmetry at its inflection point of minimum diameter. The length of the side of cone between the bases is equal to l, the distance along the axis between each large base and the central plane equal to H, and: H2 = R2 + l2 Sin =h1/l where H = (0.521-R)2 + (0.57)2, BC=R, and l = (0.521-R + R2 - h22)2 +(h1)2 H = h1 + h2 Where h1=height of cones between bases, and h2= axial distance along central axis between each smaller base and the central plane.