Critical Flare Rates for W-Beam Guardrail-Determining Maximum Capacity using Computer Simulation NCHRP 17-20(3)
Beau Kuipers, Ronald Faller, John Reid
Strong-post, W-beam guardrail systems are allowed to be installed with a flare rate up to 15:1. By increasing the flare rate, there is a possibility that overall costs can be reduced, while safety is improved. Thus, the Midwest Roadside Safety Facility has begun a multi-phase project to study flare rates. The portion of the overall project described in this report determines the maximum capacity (i.e., critical flare rate) for both the G4(1S) system and Midwest Guardrail System (MGS). A literature review on flare rates and relevant W-beam crash testing is provided, followed by detailed analysis, using BARRIER VII computer simulation, to determine critical flare rates. During the simulation process, it was deemed necessary to evaluate two possible scenarios for the MGS system: (1) using baseline post properties and (2) using early release post properties resulting from an increased impact severity. The early release post properties were deemed to be the worst case scenario. A critical flare rate of 13:1 was determined for both the MGS and modified G4(1S) system. Barrier deflection and wheel-to-post overlap (i.e., wheel snag) were the primary criteria used to determine the critical flare rates. For both systems, the critical impact point was determined to be 9.375 in. upstream of post no. 12.
Highway Safety, Flare Rates, W-beam, Computer Simulation