B G Pfeifer

DEVELOPMENT OF A NEW GUARDRAIL SYSTEM

The W-beam guardrail system has been the standard in the United States since the late 1950s and has proved to perform reasonably well under most impact conditions. However, in recent years the vehicle fleet has changed to include a relatively large percentage of light trucks, such as pickups, vans, and sport-utility vehicles. These vehicles have a higher center of mass and bumper mounting height than conventional automobiles and have been shown to have higher rollover and injury rates during guardrail accidents than conventional automobiles. Standard W-beam guardrails were not designed to capture the bumper of many of these vehicles. In recognition of the potential safety problems associated with light-truck accidents, safety performance standards were recently changed with the publication of NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. These performance standards require all new safety hardware to be tested with a full-size three-quarter-ton pickup to ensure acceptable performance for most vehicles in the light-truck category. In recognition of this, a guardrail system capable of capturing and redirecting a larger range of vehicle types and sizes was developed. A new guardrail system, called the Buffalo Rail, was designed with a new cross-sectional shape with an effective depth of 311 mm (compared to 194 mm for the W-beam), a rail thickness of 13 gauge, and a post spacing of 2500 mm. The safety performance of the Buffalo Rail was found to be acceptable according to the procedures and criteria recommended for the three-quarter-ton pickup truck at Test Level 3 in NCHRP Report 350.

Development of metal-cutting guardrail terminal

A crashworthy terminal for strong-post W-beam guardrail systems was developed at the Midwest Roadside Safety Facility at the University of Nebraska—Lincoln. The terminal incorporates an impact head that is placed over the end of a tangent section of W-beam rail. The impact head is designed to be pushed down the rail and to dissipate impact energy by cutting the W-beam along the peaks and valley to produce four essentially flat strips of steel. These flat strips are then deflected out of the path of the vehicle, striking the end of the rail. Static and dynamic component tests as well as full-scale developmental crash tests conducted during the development of this system are described. Finally, the results of the three full-scale compliance crash tests are presented and discussed. The metal-cutting guardrail terminal was shown to meet NCHRP Report 230 safety performance standards.

NCHRP REPORT 350 COMPLIANCE TESTING OF THE BEAM-EATING STEEL TERMINAL SYSTEM

An energy-absorbing guardrail terminal was developed at the Midwest Roadside Safety Facility in 1994 that met the safety criteria set forth in NCHRP Report 230. This terminal, known as the beam-eating steel terminal, or BEST, relies on the cutting of steel W-beams to absorb the energy of impacting vehicles. Since that time, a new set of safety standards has been developed to replace those set forth in NCHRP Report 230. These new criteria are published in NCHRP Report 350, with the most significant change being the replacement of the 2041-kg (4,500-lb) sedan test vehicle with a 2000-kg (0.75-ton) pickup. To ensure that the BEST system would perform well under these new, and more stringent, criteria, the system was subjected to the matrix of full-scale vehicle crash tests required by NCHRP Report 350. Several design changes were made to the terminal system during this development to improve the performance of the system. The results of this successful program are reported.