Midwest Guardrail System for Long-Span Culvert Applications

Long-span guardrail systems have been recognized as an effective means of shielding low-fill culverts. These designs are popular because, in comparison with other systems that attach posts to the top of the culvert, they are able to shield the culvert safely while creating little additional construction effort and limiting the damage to the culvert and the need for repair. However, previous long-span designs were limited by the need to use long sections of nested guardrail to prevent rail rupture and by the need for large lateral offsets between the barrier and the culvert. The Midwest Guardrail System (MGS) long-span design eliminates those two shortcomings by applying the benefits of the MGS to a long-span design. The MGS long-span design increased vehicle capture and stability because of the increased rail height, limited the potential for pocketing and wheel snag through the use of controlled-release terminal posts adjacent to the unsupported span, and greatly increased the tensile capacity of the rail through the movement of splices away from the posts and the use of shallower post embedment. These features allowed the system to be developed without the use of a nested guardrail and with a minimal barrier offset that placed the back of the guardrail posts even with the front face of the culvert. Two full-scale crash tests were conducted with the MGS long-span design according to the requirements in NCHRP Report 350 for Test Level 3 Test Designation 3-11. Both tests were conducted with the heavier 2,270-kg pickup truck to generate higher rail loads and dynamic deflections. The MGS long-span design met all safety requirements of NCHRP Report 350. The ability of the guardrail with the MGS long-span design to perform safely without a nested rail and a minimal barrier offset makes this new barrier a functional and safe option for the protection of low-fill culverts.