A road shoulder is an area that is next to a traffic lane that isn't bordered by kerb and channel. It is usually unsealed, of a lesser depth and often constructed of inferior material than the adjacent traffic lane.
Generally, it is best to drive on a road shoulder if the traffic is slow or if you need to pull over for an emergency. When the road is busy, it can be dangerous to use the shoulder as a place for stopping because of the chance of running into other vehicles.
Shoulders improve capacity by providing enough width for crash avoidance, storage of disabled vehicles, maintenance activities, and enforcement (Figure 7). They also provide a space for law enforcement personnel to carry out their duties.
Shoulder widths should be based on the anticipated traffic volume. Shoulders should be at least 4 feet (1.2 meters) wide on freeways and Interstates that have three lanes, and 10 feet (3.0 meters) wide on those with six or more lanes.
On rural minor routes classified as low-volume (less than 400 AADT), paved shoulders should not be provided. This is because the roads provide a poor level of service and have a higher crash rate than similar roadways with shoulders.
