00460154

Monograph

The purpose of this study was to evaluate the performance of naive drivers in negotiating pavement edge drops from a scrubbing condition. Two vertical heights were used (3.0 and 4.5 inches), two shapes (vertical and a 45-degree bevel), two vehicle sizes (large and small), both front- and rear-wheel drive, and hard and soft shoulders. Various speeds were used. The criterion for "failure" in the recovery maneuver was intrusion beyond the 12-foot lane adjacent to the edge drop. The results indicate that a drop of the magnitude of 4.5 inches cannot be safely negotiated at speeds as low as 20 mph. The 3.0-inch drop could be generally safely negotiated at speeds of 30 mph, but only in the largest of the three test vehicles used. Performance was poorer in the two small vehicles, indicating that speed limits should be set at no more than 25 mph in areas where edge drops of this magnitude exist. Differences between the front- and rear-wheel drive vehicles were inconsistent, and will require further study. Soft shoulders increase the effective height of the edge to be climbed, but effects associated with drag, etc. appear to be minor. In repeated trials, subjects showed some improvement in performance but, at best, they fell far short of the performance of a professional driver. Using the 45-degree bevel edge, subjects consistently negotiated it successfully at speeds up to 55 mph, the highest tested. The results of this investigation, together with other available data, indicate that pavement edge drops pose a considerable hazard to drivers who attempt recovery from a scrubbing condition. Rounded or beveled pavement edges seem to greatly reduce the hazard. There are presently no definitive data on the maximum safe height for a vertical edge drop at freeway operating speeds.

UMTRI-86-33
HS-040 380

DOT-3262-5-003(B)

69 p.

1986-7

Automated vehicle control; Driver performance; Drivers; Driving; Dropoffs (Pavements); Handling characteristics; Hazards; Height; Motor vehicles; Pavements; Personnel performance; Speed; Speed limits; Traffic speed

Edges; Pavement/shoulder drop-off

Design; Highways; Pavements; I22: Design of Pavements, Railways and Guideways; I23: Properties of Road Surfaces

HSL, TRIS, TRB

Dec 31 1990 12:00AM