An efficient form of crash barrier developed by the road research laboratory involves the use of tensioned horizontal members carried on relatively weak vertical supports. This report describes a series of tests carried out on wire rope barriers of this type in order to select the most suitable detailed design. Twenty-eight dynamic tests were carried out on alternative designs of barrier in which the ropes rested in vertical slots cut into the tops of weak i-section mild steel posts. Most of the tests were carried out with cars weighing 3000 lb, but in some tests concerned with optimum rope heights small vehicles and tall vehicles were used. Impact speeds ranged from 17 to 67 mile/h at nominal angles to the line of the barrier of 10 deg. And 20 deg. A further eight tests were made on a length of barrier erected on the 15 ft. Wide central reservation of an unopened motorway, to determine how barrier deflection for a specific impact was influenced by the length of rope between anchorages, the rope tension, and the post spacing. In this series of tests cars weighing 3000 lb struck the barrier at about 60 mile/h and 20 degrees. The optimum design is a compromise between the requirements for small and tall vehicles. It consists of two 3/4 in diameter steel ropes resting one upon the other at a height of 25 in. In vertical slots 4 1/2 in. Deep cut into the tops of 3 x 1 1/2 in. I-section steel posts spaced 8 ft. Apart. The ropes are tensioned to 3000 lb. At 50 f after being prestretched, and each rope is anchored every 2000 ft. In such a way that a colliding vehicle releases the connection between rope and anchorage. The barrier is intended for use on central reservations at least 15 ft. Wide, and with horizontal radii of curvature not less than 2800 ft. The surface of the central reservation should be hardened in order to control the height of the ropes. /RRL/A/.
Abstract