Evaluation of Flared Approach Guardrail Transitions: Test No. FLAGT-2
REPORT NUMBER
TRP-03-439c-25
AUTHORS
Scott Rosenbaugh, Ronald Faller, Bob Bielenberg, Jennifer Rasmussen (Schmidt)
PUBLICATION DATE
2025-12-12
ABSTRACT
Approach guardrail transitions (AGTs) are typically installed tangent to the roadway. However, there was a desire to install AGTs flared away from the roadway to satisfy geometry constraints or to shorten system lengths. Previously, LS-DYNA simulations were used to explore the performance of AGTs flared away from the roadway, and a 15:1 flare rate was identified as the critical maximum flare rate. A crash test on a flared AGT was conducted in accordance with the Test Level 3 (TL-3) criteria of the American Association of State and Highway and Transportation Officials’ (AASHTO) Manual for Assessing Safety Hardware (MASH). Test no. FLAGT-1, a MASH test designation no. 3-21 test, was conducted with the 2270P pickup impacting an AGT flared away from the roadway at a 15:1 rate. The selected AGT configuration had previously passed MASH TL-3 in a tangent layout. However, the 15:1 flared AGT test resulted in vehicle snag at the upstream end of the concrete buttress, which caused excessive occupant compartment deformations and excessive longitudinal ORAs. Thus, the test failed to meet MASH standards.
As documented herein, the research project continued by redesigning the flared AGT to strengthen the barrier, reduce system deflections, and mitigate vehicle snag at the end of the buttress. The redesigned system continued the use of a 15:1 flare, but the 6.5-ft long W6x9 posts on the downstream end of the AGT were replaced with larger 7.5-ft long W6x15 posts. MASH test designation no. 3-21 was then re-run on the downstream end of the redesigned system.
In test no. FLAGT-2, the 5,000-lb pickup truck impacted the system at 62.6 mph and angle of 25.4 degrees relative to the roadway (effectively 29.2 degrees relative to the flared system). The vehicle was successfully contained and redirected. Vehicle decelerations, ORAs, and OVIs all fell within the MASH limits. However, deformations to the toe pan area were 9.9 in., which exceeded MASH limits. Therefore, test no. FLAGT-2 failed to satisfy the safety criteria for MASH test designation no. 3-21.
As documented herein, the research project continued by redesigning the flared AGT to strengthen the barrier, reduce system deflections, and mitigate vehicle snag at the end of the buttress. The redesigned system continued the use of a 15:1 flare, but the 6.5-ft long W6x9 posts on the downstream end of the AGT were replaced with larger 7.5-ft long W6x15 posts. MASH test designation no. 3-21 was then re-run on the downstream end of the redesigned system.
In test no. FLAGT-2, the 5,000-lb pickup truck impacted the system at 62.6 mph and angle of 25.4 degrees relative to the roadway (effectively 29.2 degrees relative to the flared system). The vehicle was successfully contained and redirected. Vehicle decelerations, ORAs, and OVIs all fell within the MASH limits. However, deformations to the toe pan area were 9.9 in., which exceeded MASH limits. Therefore, test no. FLAGT-2 failed to satisfy the safety criteria for MASH test designation no. 3-21.
KEYWORDS
Highway Safety, Crash Test, Roadside Appurtenances, Compliance Test, MASH 2016, Test Level 3, Approach Guardrail Transition, AGT, Flare, Flared Guardrail
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