Breakaway supports for luminaires are usually a cast-aluminum transformer-type frangible base, a slip base, or frangible couplers. These devices have been developed to activate when loaded in shear by impacts at a bumper height of about 20 in (500 mm). If the supports are located so that they may be impacted at a greater height, the performance may not be as intended. Thus, foreslopes between the roadway and the support should be limited to 1:6 or flatter. The mast arm of a falling support will usually rotate away from the roadway. However, the danger of falling poles striking pedestrians, bicyclists, and other motorists should be considered.
Breakaway supports are suitable for poles that do not exceed 60 ft (18.5 m) in height and 1000 lb (450 kg). Foundations must be designed for the surrounding soils to prevent the foundation from pushing through the soil. From a roadside safety perspective, a preferred method for lighting major intersections is to use high-mast lighting, because fewer supports are required and they can be located farther from the roadway. Supports located in the clear zone should be protected with a suitable traffic barrier.
