Limits of Acceptable Rail-and-Post Deflection in Crash-Damaged Strong-Post W-Beam Guardrail

the supporting posts and soil. Impacts with a higher speed but shallower angle can also cause more distributed rail-and-post deflection. The amount of deflection that can be sustained by guardrail before its safety is compromised is a major concern. Maintenance crews and highway agencies are often forced to balance the expense of continual repairs against the potential liability if the damaged guardrail is struck again. A recent survey of U.S. states and Canadian provinces revealed that very few agencies have quantitative criteria underlying the decision of when to replace deflected guardrail (2, 3). Among those agencies that do, the threshold deflection was most commonly set at 6 in. (152 mm) of deflection. This is also the recommended repair threshold for minor deflection specified by the FHWA (4). Individual agencies (2, 3) had thresholds as low as 3 in. (76 mm) or as high as 12 in. (305 mm). This study is intended to test the performance of guardrail with rail-and-post deflection to support a unified repair threshold for deflection on the basis of quantitative data. Currently, all guardrail systems are thoroughly crash tested according to the testing procedure and thresholds specified in NCHRP Report 350 (1). NCHRP Report 350 provides a variety of measurable criteria with which the performance of the guardrail can be assessed. These criteria were divided into three categories: structural adequacy, occupant risk, and post impact vehicle trajectory. Guardrail meeting the requirements of all three categories should be accepted by the FHWA for installation on the national highway system. However, guardrail systems that have suffered minor deflection damage may no longer meet the same criteria and would require repair to restore functionality.