Current Minnesota Department of Transportation (Mn/DOT) design practice for many traffic signals utilizes an arrangement of steel guard posts to protect the signal, and in particular the signal head, from short turning vehicles. None of the components (guard post or traffic signal support) had been evaluated for automobile impacts and Mn/DOT was concerned about the performance of these installations. Accordingly, a project was initiated to determine the performance of the guard post/signal support installation when impacted by a 1800-lb (800-kg) class vehicles.
Pendulum testing was used to evaluate the guard post and signal supports separately. It was determined that the signal support performed satisfactorily whereas the guard post would require modification to perform satisfactorily according to current recommended acceptance criteria.
Performance criteria were determined for the modified guard post and two different concepts were evaluated in pendulum and vehicle crash tests. The guard post design using a breakaway steel coupling is recommended for installation with the standard signal support based on satisfactory crash test results using 1800-lb (800-kg) Hondas impacting the installation at 20 (32) and 60 (95) mph (km/h).
