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NCHRP 350 DEVELOPMENT AND TESTING OF A GUARDRAIL CONNECTION TO LOW-FILL CULVERTS

In this research, a W-beam guardrail system was developed for installation with the steel post attached to the top of a low-fill concrete culvert. The guardrail system was constructed with a 2.66-mm (12-gauge) thick W-beam rail totaling 53.34 m in length. The post spacing was 1,905-mm on center for post numbers 1-9 and 33-41, while the post spacing for post numbers 9-33 was 952.5-mm on center. Two full-scale vehicle crash tests, using 3/4 ton pickup trucks, were performed on the W-beam guardrail system. One test was successfully conducted on the guardrail system with the backside of the posts positioned 457 mm from the front face of the culvert's headwall. The second test was unsuccessfully performed on the guardrail system with the backside of the posts positioned 25 mm from the front face of the headwall. The tests were conducted and reported in accordance with the requirements specified in the National Cooperative Highway Research Program (NCHRP) Report No. 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. The safety performance of the W-beam guardrail system attached to the top of a low-fill concrete culvert was determined to be acceptable according to the NCHRP criteria. From an analysis of the crash test results, findings indicate that the backside face of the steel posts can be positioned a minimum of 254 mm away from the front face of the culvert's headwall and still maintain acceptable barrier performance.