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Development of the Midwest Guardrail System (MGS) W-Beam to Thrie Beam Transition Element




Craig Eller, Karla Lechtenberg (Polivka), Ronald Faller, Dean Sicking, John Rohde, John Reid, Bob Bielenberg, Erin Allison




For longitudinal barriers, it is common practice to use standard W-beam guardrail along the required highway segments and to use a stiffened thrie beam guardrail in a transition region near the end of a bridge. As a result of the differences in rail geometries, a W-beam to thrie beam transition element is typically used to connect the two rail sections and to provide continuity in the barrier system. However, the W-beam to thrie beam transition element has not been evaluated according to current impact safety standards. Therefore, an approach guardrail transition system, including a W-beam to thrie beam transition element, was constructed and crash tested. The transition system was attached to Missouri's thrie beam and channel bridge railing system. The objective of the study was to evaluate the safety performance of a W-beam to thrie beam transition element according to the Test Level 3 (TL-3) criteria set forth in the NCHRP Report No. 350. The research study included four full-scale vehicle crash tests, three with a -ton pickup truck and one with a small car. Due to vehicle rollover of the first pickup truck test, the W-beam to thrie beam transition was redesigned to consist of an asymmetrical W-beam to thrie beam transition element and an increase in W-beam height to the Midwest Guardrail System (MGS) height of 787 mm (31 in.). Following the successful redirection of the -ton pickup truck and the small car, the safety performance of the asymmetrical MGS W-beam to thrie beam transition element was determined to be acceptable according to the TL-3 evaluation criteria specified in NCHRP Report No. 350.


Highway Safety, Guardrail, Roadside Appurtenances, Longitudinal Barrier, Crash Test, Compliance Test, W-Thrie Beam Transition, Midwest Guardrail System

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