Clear zone widths in the , which is the basis for guidance in the RDM, are calculated using a passenger car or truck as the design vehicle. A clear zone for a motorcycle might need to consider a motorcyclist who has been thrown from his or her bike, making it uncertain if the AASHTO clear zone widths are adequate. A wider clear zone is better because it allows a motorcyclist more distance to decelerate before striking a roadside feature.

Motorcycles differ from other vehicles in that they overhang their wheel track by about 1-ft to 2-ft on each side and because they lean to change direction, which markedly alters the Table of Contents Instructions Reference Links Roadway Design Manual | 20-8 clearance they require when travelling upright. Failure to account for these characteristics may result in riders colliding with poles, signs, or fences that are placed too close to the edge of the pavement.

When objects cannot be located outside the clear zone, agencies have recommended a variety of methods to minimize risk to motorcyclists including: