The extent of the problem of accidents involving vehicles on shoulders of limited-access highways was quantified. Accident data for a 3-year period, 1985 through 1987, were collected along with a survey of vehicles stopped on the shoulder on interstates and parkways. Although the percentage of all accidents on interstates and parkways involving a vehicle on the shoulder is small (1.8%), The percentage of fatal accidents involving a vehicle on the shoulder is significant (11.1%). The accident data revealed that the majority of shoulder vehicles had stopped for an emergency stop, as opposed to a leisurestop, with a large number involving an abandoned vehicle; the most common reason for stopping was mechanical failure; tractor-trailers were overrepresented in shoulder accidents; an unusually high percentage occurred in the time period of midnight to 6 a.m. The major contributing factors were alcohol involvement and the driver on the mainline falling asleep. Two types of observational surveys were taken. One survey represented what a driver would observe while driving from one point to another on an interstate or parkway. This survey indicated that a driver would pass (in his direction of travel) an average of about one vehicle on the shoulder every 8 miles on an interstate and every 17 miles on a parkway. The second survey was conducted in a circular route so that almost all stops would be observed. The highest percentage of stops were over 1 hour in length.
Abstract