Extending TL-2 Short-Radius Guardrail to Larger Radii
Cody Stolle, John Reid, Bob Bielenberg, Ronald Faller, Dean Sicking, Karla Lechtenberg
Longitudinal barriers are commonly used to shield hazards including bridge rail ends, bridge parapets, and slopes. In some locations, a secondary roadway intersects the primary roadway within the guardrail's length-of-need (LON). Some intersections have radii as large as 72 ft (22 m) between primary and secondary roadways, which require untested modifications to existing short radius guardrail systems. No short radius systems have been tested and approved to shield hazards with these conditions. A validated computer simulation model of the Yuma County system was modified and simulated with larger radii of 24, 48, and 72 ft (7.3, 15, and 22 m) using a 2000P vehicle in LS-DYNA. Impacts with 27-in. (686-mm) tall systems frequently resulted in vehicle vaulting when impacted at 45 mph (72 km/h), although blockouts reduced vaulting and increased system effectiveness. Maximum practical speeds to utilize 27-in. (686-mm) tall curved guardrail systems with blockouts were 19, 22, and 23 mph (31, 35, and 37 km/h) for radii of 24, 48, and 72 ft (7.3, 15, and 22 m), respectively. Maximum practical speeds without blockouts were 29, 26, and 41 mph (47, 42, and 66 km/h), respectively. Blockouts reduced vaulting by maintaining rail height, reducing tire interaction with post debris, and facilitating easier rail release via post twisting. A 29-in. (737-mm) tall system with blockouts and a 31-in. (787-mm) tall system without blockouts performed acceptably at 45 mph (72 km/h) and 25 degrees, downstream of the beginning of the Length-of-Need (LON).
Highway Safety, Roadside Appurtenances, Short-Radius Guardrail, Simulation, LS-DYNA, Curved Guardrail, Intersection, and NCHRP Report No. 350