- Shoulder width and lane width can impact both safety and mobility. Shoulders provide a stable and clear recovery area for drivers who have left the travel lane and a place for a driver to maneuver to avoid crashes. They also provide an area for law enforcement to safely pull vehicles over, a place to provide safer bicycle accommodation, and a place for disabled vehicles to pull over. Lane width can influence crashes related to lane departure. AASHTO's policy on geometric design on highways and streets has established ranges for minimum shoulder widths for various types of roadways to help maximize safety and mobility. However, current studies have mixed conclusions as to what effect width has on safety. The evaluation of Idaho-specific data with respect to shoulder width and lane width and their impact on safety would be helpful in providing additional information for the determination of future projects.