NCHRP 350 Development and Testing of a Guardrail Connection to Low-Fill Culverts
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ABSTRACT
A W-beam guardrail system was developed for installation with the steel posts 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 W-beam rail was supported by twenty-four W152x13.4 by 1,829-mm long steel posts and thirteen W152x13.4 by 946-mm long steel posts. The post spacing was 1,905-mm on center for post nos. 1 through 9 and 33 through 41, while the post spacing for post nos. 9 through 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 Test Level 3 (TL-3) evaluation criteria specified in NCHRP Report No. 350. From an analysis of the crash test results, it is recommended 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.
KEYWORDS
Highway Safety, Guardrail, Longitudinal Barrier, Box Culvert, Roadside Appurtenances, Crash Test, Compliance Test