Guardrail Optimization for Rural Roads

Guardrail barriers are optimized to provide a recommended lower-cost barrier solution for rural roadways in the United States, Europe, and developing countries. Physics-based guardrail analysis has determined that barrier behaviors are not random but tend to follow consistent characteristic patterns of response to vehicle impacts. Performance variability in conventional W-beam guardrails is closely associated with components that introduce variability into these patterns. Independent variations in release load of around 360% and 40% combine to result in the three primary guardrail failure modes, known as vehicle pocketing, vaulting, and hard wheel snagging. The solution to this performance variability problem is to optimize the release load in relation to support-post-section properties. This operation is accomplished by introducing a separate deformable release member that consistently provides the needed release load. This procedure enables the simultaneous optimization of cost and performance by reestablishing stable patterns in guardrail response to vehicle impacts; addressing the three primary guardrail failure modes; eliminating complexity associated with unnecessary components such as offset blocks, backup plates, and midspan splices; upgrading the reliability of existing guardrail systems on a retrofitable basis with minimal disruption; enabling a range of standard post types to accommodate local material preferences; and enabling a range of post spacings for diverse terrains and a range of rail heights to accommodate roadway overlays. A versatile W-beam guardrail incorporating these improved capabilities has been successfully crash tested and accepted by FHWA at NCHRP Report 350 test levels and Test Level 3 of the AASHTO Manual for Assessing Safety Hardware.