Abstract
Previous studies have found that steering is quite robust to reduced luminance; when traveling at a constant speed, older drivers' steering performance is poorer than younger drivers' (Owens & Tyrrell, 1999.) The current study examined the preferred driving speed of 11 older (M=72.5 years) and 10 younger (M=19.6 years) licensed drivers under 5 luminance conditions (−3 to 1 log cd/m2.) Participants drove a simulator on continuously-curvy rural roadways with a 55-mph speed limit. Each participant was encouraged to drive at his or her preferred speed while remaining within their lane; at the conclusion of each trial, workload was rated on a 0–150 scale. The drivers' steering ability was robust; the percentage of the trial the vehicle was entirely within the lane ranged from 92% in the maximum luminance condition to 71% in the darkest condition, despite a 4-log-unit luminance reduction. While there was no difference between the older and younger drivers' steering ability, age differences were present for preferred driving speed. Averaged across the luminance conditions, the older drivers traveled more slowly (39.5 mph) than the younger drivers (52.5 mph.) Averaged across age groups, speed decreased from 51.3 mph in the maximum luminance condition to 37.6 mph in the darkest condition. The speed gap between the age groups increased as luminance decreased, with the smallest difference (8.1 mph) in the maximum luminance condition and largest difference (16.5 mph) in the minimum luminance condition. As luminance decreased, the drivers' workload significantly increased from 36.2 in the maximum luminance condition to 84.5 in the darkest. There was no difference between the age groups' self-reported workloads.
This work was supported by the National Science Foundation and the Department of Defense ASSURE Program under Grant No. SES-0353698.