A passenger car, highway maintenance truck, or a barricade was placed on the shoulder at the pavement edge and at 3 feet and 6 feet from the pavement edge. Observations of the effect were recorded on two-lane and four-lane divided highways. During light-to-moderate traffic volumes on the wider two-lane highways and on four-lane highways, vehicle speeds were affected little, if at all, by the objects on the shoulder. However, on two-lane pavements 20 feet or less in width, speeds averaged approximately 3 mph. Lower with vehicles or barricades on the shoulder. The transverse positions were affected only for those vehicles moving in the lane adjacent to the shoulder on which the vehicle or barricade was placed. The narrower the pavement and the closer the object to the pavement edge, the greater was the lateral displacement of vehicles from their normal path. An object placed at the edge of an 8-foot lane of a two-lane highway caused vehicles to travel 3.3 feet farther from the pavement edge than when the object was not present. On a 12- foot lane the corresponding value was 1.8 feet. Objects on the shoulder of a four-lane divided highway had a slightly lesser effect than on two-lane highway. When the vehicle or barricade was placed 6 feet from the pavement edge, no significant effect on the transverse positions of moving vehicles was found. A car, truck, or barricade parked on the shoulder each had about the same effect on vehicle speed and lateral position, except for the slightly lesser effect of the barricade on the four-lane highway. /author/ same effect on vehicle speed and lateral position, on vehicle speed and lteral position, except for the slightly lesser effects of the barricade on the four- lane highway. /author/.
Abstract