Performance of the Midwest Guardrail System with Rectangular Wood Posts

Abstract

Strong-post W-beam is one of the most enduring and prolific safety barriers in the world. Over the years, it has been modified and updated to improve performance. Throughout these changes, two types of guardrail posts have been used to support the rail element: W6 × 8.5 steel posts and 6-in.-wide × 8-in.-deep wood posts. Recent updates to roadside safety hardware evaluation criteria and concerns with the performance of the G4 (1S) and G4 (2W) strong-post W-beam systems have led to the need for enhanced strong-post guardrail designs. The Midwest Guardrail System (MGS) was developed to address this need and provides improved performance over previous strong-post W-beam systems. The MGS was developed and tested with steel support posts, and it was believed that the use of wood posts in the system would provide similar barrier performance. However, the effect of wood posts in the MGS was never quantified through full-scale crash testing. The objective of this study was to investigate and evaluate the performance of the MGS with rectangular posts made of southern yellow pine. This effort included a review of the performance of wood and steel guardrail posts as it pertained to the MGS, the completion of two full-scale crash tests according to the Manual for Assessing Safety Hardware (MASH) safety requirements, and a comparison of the full-scale test results with MASH safety criteria and previous steel-post and alternative species wood-post MGS tests. Finally, recommendations were developed to implement the wood-post MGS and wood posts in MGS special applications.