Analysis of Sign Attachments to Breakaway Luminaire Supports
Ryan Nelson, Dean Sicking, Karla Lechtenberg
Removal of fixed objects is one of the most basic methods for improving roadside safety. Although breakaway signs and luminaire supports are generally considered to be relatively minor hazards, combining these systems has been proven to be a cost effective approach to improving roadside safety. In order to reduce the number of roadside obstacles, small roadside signs can be attached to luminaire supports. The large mass associated with luminaire supports and the high forces required to activate large breakaway devices are the primary considerations associated with the system's safety performance. Consequently, luminaire supports are subjected to high decelerations when struck by errant vehicles. The rapid acceleration of the luminaire support could cause the sign panel to become detached and pose a potential hazard to vehicle occupants. A study was undertaken to determine the connection strength required to assure that sign panels remain attached to luminaire supports subjected to high-speed impacts. Most small signs are fabricated from aluminum sheeting and are limited to a maximum size of approximately 1.5 m2 (16 ft2) due to the bending strength of the panel. Since sign panel mass increases with sign area, the larger signs will generate high connection loads. Furthermore, luminaire support accelerations are inversely related to size of the support. Several combinations of vehicle and support geometries and properties were investigated to assess a critical design case. Maximum connection loads were found to be associated with 1.2 m x 1.2 m (4 ft x 4 ft) sign panels mounted on short, 5.2-m (17-ft) tall, luminaire supports. Finally, recommendations were made pertaining to the connection devices used to keep the sign panels attached along with recommendations on attaching sign panels to very tall luminaire supports.
Highway Safety, Breakaway Luminaire Supports, Sign Attachments, Roadside Appurtenances, Compliance Test