This study was conducted to quantify the extent of the problem of accidents involving vehicles on shoulders of limited access highways. Accident data for a three-year period (1985-1987) were collected along with a survey of vehicles stopped on the shoulder on interstates and parkways.

While the percentage of all accidents on interstates and parkways involving a vehicle on the shoulder is small (1.8 percent), the percentage of fatal accidents involving a vehicle on the shoulder is significant (11.1 percent). The accident data revealed that the majority of shoulder vehicles had stopped for an emergency stop as opposed to a leisure stop with a large number involving an abandoned vehicle. The most common reason for stopping was a 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. It indicated that a driver would pass (in his direction of travel) an average of about one vehicle on the shoulder every eight miles on an interstate and every 17 miles on a parkway. The second survey was conducted in a circular route such that almost all stops would be observed. The highest percentage of stops were over one hour in length.

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The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, of the Kentucky Transportation Cabinet, nor of the Federal Highway Administration. The report does not constitute a standard, specification, or regulation.