North Dakota uses the type G3 box beam roadside barrier with minor modifications thereto. The box beam has been chosen because of its narrow profile and low resistance to wind forces and snow drifts. There is no acceptable narrow profile end treatment, and the North Dakota State Highway Department was seeking a relatively simple and inexpensive treatment which would eliminate or greatly reduce the probability of vehicle ramping or rolling. Testing by the Texas Transportation Institute indicates that an acceptable solution has been developed. An American Standard Channel-C7 x 9.8-60 ft (18.3 m) long was utilized in the modified final design of the end treatment. A permanent 90 deg twist was made so that the channel web would be vertical at the first post and horizontal at the foundation with the flanges pointing down. This section was then pushed to the ground offset 2 ft (0.6 m) away from traffic and attached to a concrete footing centered 24 ft (7.3 m) from the first post. The post at the beginning of the length of need was a brittle 6 in. by 6 in. wood post. The second post was located 12 ft (3.7 m) downstream and all posts were then spaced at 6 ft (1.8 m). All posts except the first were S3 x 5.7 steel. The action of this modified rail terminal is quite simple. When a vehicle tire or bumper pushes down on the turned-down terminal the rail will quickly drop from the first 8 posts allowing the vehicle to pass over the rail without the violent ramping effect of a rigid turn down. (FHWA).
Samenvatting