Civil Engineering


Date of this Version





The breakaway luminaire support concept has existed for many years and has proven to be an effective safety device. The 4-bolt breakaway slipbase design was originally used in Utah and has been used successfully in 20 years of field implementation. The state transportation departments of Idaho, Montana, Nevada, Utah, and Wyoming requested that the 4-bolt slipbase system be evaluated for possible use on Federal-aid highway projects. Two full-scale vehicle crash tests were performed by the Midwest Roadside Safety Facility to evaluate the system. Both tests had a centerline impact location. Test USBLM-1 was conducted with a 1,800-lb vehicle traveling at 15 mph. and Test USBLM-2 was conducted with a 1,800-lb vehicle traveling at 57.5 mph. The fullscale vehicle crash tests were evaluated according to the performance criteria presented in NCHRP Report 230 and the 1985 AASHTO specifications for structural supports. The Code of Federal Regulations, in which FHWA slightly modified the AASHTO requirement for maximum allowable change in velocity, was also used in the evaluation (23 CFR 625). The tests easily met all of the performance criteria mentioned above. Therefore. the safety performance of the 4-bolt breakaway slipbase design was determined to be satisfactory.