PAVEMENT EDGES, CHAPTER 4

The results of published studies on the influence of longitudinal pavement edges on vehicle safety are consistent and supplement each other. It is agreed that loss of vehicle control can develop at speeds greater than 30 mph under certain circumstances, where inattentive or inexperienced drivers return to the traffic lane by oversteering to overcome the resistance from a continuous pavement edge and tire-scrubbing condition. This safety problem is minimized where the pavement edge drop does not exceed 3 in. in height or the face has a 45-degree slope. A loose or muddy soil shoulder should not increase the edge-climbing difficulty, provided that the overall height is the same. However, similar-looking losses of control can occur even without any edge drop when an errant vehicle is returned to the higher surface friction of the pavement by oversteering. Pavement edge heights more than 5 in. in height can interfere with the underneath clearance and thus create safety problems for small automobiles. (Author)