Accident rates increase steadily per mile driven beyond age 60. In addition, the older body is generally weaker and less likely to survive a traumatic accident, possibly contributing to a greater crash fatality rate among older persons, making motor vehicle crashes the leading cause of death from unintentional injury for those aged 65 to 74. This increased accident rate is largely accidents incurred when making left hand turns. If the reason for these left turn accidents could be identified, then a preventative effort could possibly be designed. In a series of published and unpublished (Quillian et al., The effects of age and alcohol intoxication on simulated driving performance, awareness, and self-restraint) studies employing a driving simulator, we have reported that older drivers do not spend more time than younger drivers at the stop line of a left turn. This suggests that age is not associated with longer decision making concerning when to rum. However, older people do spend significantly longer executing the left hand turn. This is consistent with the general tendency of older drivers to drive slower as a compensatory strategy. In making a left hand turn, the driver has to drive through potential traffic coming from ahead, right, and left. However, the longer the driver spends crossing these three lines of traffic, the greater the driver's exposure to this high-risk situation. To verify realistically the simulation results that older drivers take longer executing a left turn, we had two observers sit at an intersection, estimate the age of the driver as s/he pulled up to the stop line, and then time the driver from the point of leaving the stop line to passing a white pole located 60 feet into the left turn beyond the intersection. The intersection was a through way for North-South traffic and a stop sign for East-West traffic. We timed drivers coming from the West and turning North, which meant drivers coming to the stop sign and turning left across oncoming traffic. Seventy drivers were timed over two 1-hour samples, once on a Saturday and once, a week later, on a Sunday. Because we wanted natural behaviours, we could not ask a driver's age before the turn and could not safely stop him/her after the turn. Consequently, the two raters estimated the driver's age, and when there was a disagreement, a mutual consensus was reached. Subjects were classified into one of three distinct groups: Young, Mature, and Older drivers. Young drivers were estimated to be less than 25 years of age, Mature drivers were those estimated to be between ages 35 and 55, and Older drivers were those estimated to be more than 65 years of age. To ensure non-overlapping age groups, drivers estimated to be ages 26 to 34 and 56 to 64 were excluded from data analysis. Subjects were also excluded if they drove a standard transmission, detected by hearing gears shift in the turn. There were 11, 24, and 11 Young, Mature, and Older drivers who fit the inclusion criteria. Raters' times correlated significantly (r = .96, P < .001). Because times were collected on two different days, when the position of the timers and the signal post, as well as the time of day, could have influenced turn times, scores for the two days were converted to z scores and then combined for comparisons. Therefore, a z score of 0 represents the mean turn time, and a z score of + 1 refers to a turn time that was 1 standard deviation above the mean. As seen in Figure 1, turning time was significantly different (F = 10.357, P < .0002) among the age groups. The mean z scores for Young, Mature, and Older drivers were .66, -.07, and +.95, respectively.This real observation confirms the simulation data indicating that older drivers have longer exposure to the high-risk situation of crossing three lines of traffic when making a left hand turn compared with younger age groups. If this increased exposure contributes to the increased accident rate among older drivers making left turns, it may be important to encourage older drivers to pass through left turns more quickly once the decision has been made to initiate the turn. (A)
Samenvatting