Short-Radius Guardrail System for NCHRP Report 350 Test Level 2 Conditions

When a road or driveway intersects a highway with certain restrictive features (bridge rail, culvert, etc.), it is difficult to fit the proper guardrail length (transition, length-of-need guardrail, and end treatment) along the primary roadway. Site constraints such as private driveways, state roads, and parish or county roads may intersect the primary road and prohibit the placement of a properly designed guardrail of the length needed. In these cases, the alternatives are to shorten the designed guardrail length, to relocate the constraint that is blocking placement of the guardrail, and to provide a curved or T-intersection guardrail design. This curved guardrail system is usually known as a short-radius guardrail. This paper investigated the performance of previously tested short-radius guardrail systems to determine whether some of those guardrail systems met NCHRP Report 350 Test Level 2 (TL-2) evaluation criteria. A system designed and tested for Yuma County, Arizona, was adapted as the basis for developing a short-radius guardrail system that satisfies NCHRP Report 350 TL-2 criteria. From an engineering review of previous designs, a recommended short-radius guardrail system that satisfied NCHRP Report 350 TL-2 conditions was developed. The nose section of this system consists of a 3.82-m (121/2-ft) curved W-beam segment that has a 2.44-m (8-ft) radius. This curved section is mounted on breakaway controlled-release terminal posts.