Visual Demand of Driving Curves as Determined by Visual Occlusion

The visual demand of driving was determined using the visual occlusion method. In this method, drivers pressed a switch to get a half-second glimpse of the road. Otherwise, the road was occluded. Visual demand was defined as the proportion of time the road was visible. Twenty-four licensed motorists from 3 age groups (18-24, 35-54, 55+) drove a simulated single-lane road consisting of 12 separated curves of 4 curve radii (582 m, 291 m, 194 m, and 146 m) and 3 deflection angles (20 ̊, 45 ̊, 90 ̊). Subjective ratings of demand were obtained for each curve. Based on the occlusion data, mean demand values for curves were determined. Visual demand increased significantly with the reciprocal of curve radius and increased considerably with driver age. Mean demand values were 0.34 for a straight section and 0.61 for the sharpest curves examined. Most remarkable was the considerable sensitivity of the demand profiles to curve variations, particularly given the small data set. Occlusion-based demand appears to be very sensitive to variations in road geometry and to the driver’s age.