Nighttime Curvature Perception of Drivers as a Function of the Number of Curve Delineation Devices

This exploratory study investigated the m o n d a r (4 subjects) and binocular (7 subjects) curvature perception accuracy of young drivers under curve approach and nighttime conditions in a 150 scaled laboratory set up. The experiment consisted of a sequential comparison of a 90" curve segment with a standard radius equipped with 12 equally spaced 150 scaled retro-reflective yellow/black miniature (H 12.2mm, W 9.lmm) chevrons with a 90" test curve segment which could have 2, 3, 4, or 8 equally spaced miniature chevron signs along a curve radius of 95%, 97.5%, loo%, 102.5% or 105% of the standard curve radius. For each presentation the standard curve was presented first to the subjects (black road environment, lowbeam illumination) for 2 seconds, then the subjects rotated 90" and observed the test curve (one of five curve radii, with either 2, 3, 4, or 8 equally spaced chevrons) for 2 seconds. A forced choice response (smaller, larger than the standard curve radius) was required from the subjects. All experimental conditions (5 radii, 4 chevron levels, 5 replications for each subject) were randomized for each subject. The curve approach viewing distance from the subject's eyes to the beginning of the curve was 4.57m (15 ft) which represents 228.6m or 750 ft in the real world, while the curve radius of the standard curve was .9144m or 3 ft which represents a curve radius of 45.6m or 150 ft in the real world. The overall averages for the percentage of the number of correct responses were calculated for all conditions and plotted against the number of chevrons. Based upon the results we may tentatively state that the overall average number of correct responses increases from 2 to 3 chevrons and then remains about the same for 4 and 8 chevrons. Further, the values for binocular viewing are somewhat higher for 4 and 8 chevrons. Therefore, we may tentatively conclude that for the above conditions 4 equally spaced chevrons within a total visual field of about 6" provide adequate curvature estimation cues for unfamiliar drivers approaching a curve at night.