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Evaluation of Flare Rates for Approach Guardrail Transitions – Phase I




Ryan Bickhaus, Jennifer Rasmussen (Schmidt), Bob Bielenberg, Scott Rosenbaugh, Ronald Faller, John Reid




The objective of this research study was to use computer simulation to identify the critical flare rate for flaring approach guardrail transitions (AGTs) away from the primary roadway. Installing an AGT with a flared configuration results in a reduction of the length of need (LON) as well as an increase in the clear zone area in front of the barrier, which would reduce both installation cost and accident frequency. The research focused on the determination of the maximum allowable flare rate that could safely be utilized with 31-in. (787-mm) tall thrie-beam AGTs without concrete curbs that utilize the Midwest Guardrail System (MGS) upstream of the transition. The Phase I research consisted of a literature review, development and validation of a tangent AGT LS-DYNA model, LS-DYNA simulation of multiple AGT flare rates from 10:1 to 25:1 with respect to the roadway, and the determination of the critical flare rate and critical impact points (CIPs) for full-scale testing. The simulation study identified the 15:1 (3.81 degrees from roadway) and 12.5:1 (4.57 degrees from roadway) flare rates as the critical flare rates that exhibited significant LON reduction while maintaining acceptable Manual for Assessing Safety Hardware (MASH 2016) safety performance criteria. Further simulation identified CIPs. In comparisons between the critical flare rates at the CIPs, the 15:1 flare rate exhibited improved vehicle stability and occupant risk criteria and should have a greater potential to pass MASH 2016 criteria, compared to the 12.5:1 flare rate. As a result, with sponsor feedback, the 15:1 flare rate was selected as the critical flare rate for full-scale crash testing.


Highway Safety, Crash Test, Roadside Appurtenances, Compliance Test, MASH 2016, Test Level 3, Approach Guardrail Transition, AGT, Flare, Flared Guardrail, Computer Simulation

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