The Clear Zone
The "forgiving roadside" concept recommends the development of a roadside "clear zone." A clear zone is the total roadside border area, starting at the edge of the traveled way, which is available for safe use by errant vehicles.
Clear Zone Distances
(in feet from edge of travel way)
The clear zone includes all areas along the roadside that are to be free of fixed objects and have slopes that may be safely crossed by a vehicle. The clear zone should be wide enough to allow a vehicle to regain control and return to the roadway or come to a controlled stop.
The design clear zone for a roadway is based on design speed, traffic volume, side slopes, roadway curvature, and site-specific conditions. The clear zone varies in width from 7 to 18 feet along low-speed roadways (40 mph or less) depending on ADT, from 10 to 28 feet along higher-speed facilities (45-50 mph), and up to as much as 46 feet along high-speed roadways including interstate highways.
The minimum horizontal clearance for an object adjacent to the travel way behind vertical curbing is 2 feet, but should not be construed as an acceptable clear zone. Since curbs are generally recognized as having no significant containment or redirection capability, clear zone should be based on traffic volumes and speeds, both without and with a curb.