Data for this synthesis was acquired from a questionnaire received from forty-three states in 1977. It was divided into sections on policy and procedures, design, and operations. In the area of policy and procedures, the predominant criterion used by the states to select the shoulder type, thickness, width, and slope is the combination of highway classification and traffic volume. Most of the states depend on the cross slope of the shoulders for surface drainage, but a significant number of states use some form of dikes, catch basins, or gutters. For subsurface drainage, the predominant policy is to use underdrains or a free-draining base. In the design area, most states use the same width and slope of shoulders adjacent to both rigid and flexible pavements. On freeways, nearly 80 percent of the states use a 10-ft (3-m) width for the outside shoulder. The predominant shoulder slope is 4 percent or 1/2 in. per foot. Most of the states pave the shoulders on the Interstate and major highways, but on local roads the shoulder material is often some form of aggregate, earth, or sod. In the area of operations, only five states permit regular use of shoulders for slow-moving vehicles, although 10 states permit such use under certain conditions. Shoulder maintenance is not performed on a regular schedule in most states; even in those states that have a schedule, it frequently applies only to unpaved shoulders. Little data were received on maintenance costs. Some of the recommendations of this synthesis include research into the safety effects of shoulders, particularly with respect to the types in use; evaluation of the effects of shoulder types on pavement performance; a study of maintenance costs of various types and designs of shoulders; and more definitive construction costs to enable better selection of shoulder types for given conditions.
Samenvatting