Safe placement of breakaway luminaire poles behind Midwest Guardrail System

Abstract

ABSTRACTLuminaire poles are commonly installed along highways to provide proper illumination in critical areas. When placing light poles in close proximity to guardrail, the poles may affect the guardrail's ability to safely contain and redirect vehicles. The interaction between a deflected guardrail system and a closely-positioned light pole may create unwanted stiffening or hinging of the barrier system around the pole. The pole may also present a snag hazard to impacting vehicles and induce vehicle instabilities. In this study, the barrier clearance distance, i.e. the lateral offset away from a breakaway light pole was investigated and evaluated. The minimum safe lateral offset away from the pole with respect to the Midwest Guardrail System (MGS) was determined to be 508 mm (20 in.) through crash testing and computer simulation with non-linear finite-element analysis. Two full-scale crash tests were conducted according to the American Association of State Highway Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL-3) impact safety criteria. In test no. ILT-1, a 2268-kg (5000-lb) pickup truck impacted the combination MGS with light pole system laterally offset 508 mm (20 in.) from back of posts at a speed of 100.7 km/h (62.6 mph) and an angle of 25.0°. In test no. ILT-1, the pickup truck was captured and safely redirected while impacting the light pole and disengaging the pole away from the base. In test no. ILT-2, a 1098-kg (2420-lb) small car impacted the combination MGS with light pole system laterally offset 508 mm (20 in.) from back of posts at a speed of 100.9 km/h (62.7 mph) and an angle of 25.6°. In test no. ILT-2, the car was safely contained and redirected while minimally contacting the light pole. The MGS with a lateral pole offset of 508 mm (20 in.) away from back of posts to front face of pole provided an acceptable safety performance to MASH TL-3 when critically impacted by a pickup truck and a small car. Thus, a minimum offset of 508 mm (20 in.) between the back of the MGS post and front face of the breakaway pole was sufficient to assure a safe performance of the MGS during vehicle impacts without undesired interaction with the pole. Accordingly, guidance for the safe pole placement behind the MGS was provided.