Objective:​ By 2030 it is expected the elderly will comprise 25 percent of the drivers in the United States. It is also estimated that currently in the United States alone, 500 older adults are injured each day in motor vehicle crashes (MVCs). Current research has not been able to consistently produce a direct connection between MVCs and specific age-related changes. It is speculated that crash rates are more likely linked to an interaction between driver characteristics and driving conditions as well as the driving environment. Sundowner's syndrome occurs in older drivers starting in the late afternoon through early evening (generally between 3:​00 pm and 8:​00 pm) and involves behaviors such as confusion, disorientation, and restlessness. The following retrospective study was designed to assess the frequency of older drivers admitted to a trauma service due to an MVC based on the time of day of the MVC compared to younger and middle-aged drivers.

Methods:​ The study included all adult trauma patients ≥ 21 years of age admitted to a Level 1 trauma center due to a, MVC, in which they were the driver of the vehicle, between January 1, 2005, and December 31, 2010.

Results:​ A 3 (Injury Time Period) × 7 (Age Category) chi-square was performed to assess whether there was a disproportionate number of patients admitted as a function of time of injury and age. The overall chi-square was statistically significant. Consequently, a 3 × 7 analysis of variance (ANOVA) was performed on injury severity score (ISS). Tukey's posttest revealed that ISS was highest during the early evening time period.

Conclusions:​ The evidence of the early evening time period having a differential impact on older drivers is through a demonstration of an Injury Time Period × Age Category interaction. This interaction was found to substantiate the hypothesis that older drivers have a disproportionately higher rate of injury due to an MVC during the early evening time period than younger and middle-aged drivers. In identifying the early evening's time period as a time in which older drivers are more likely to experience injury from an MVC than younger and middle-aged drivers, we believe that our research adds insight into why age restrictions have not been successful in reducing crash rates in the older driver population. It is the compound effect of age-related changes and environmental conditions that contributes to the higher proportion of MVCs. Age restrictions alone do not take into account environmental conditions.