Questionnaire-based evidence of association between sleepiness while driving and motor vehicle crashes that are subjectively not caused by falling asleep

Sleep problems and subjective sleepiness during driving have been accepted as factors associated with motor vehicle crashes (MVCs) in Western countries. However, the relation between MVCs and sleep problems or sleepiness during driving remains unclarified for a Japanese population. Moreover, little has been reported about MVC-associated factors by classifying MVCs into those caused by falling asleep and those not caused by falling asleep. In this study, a questionnaire-based cross-sectional survey was administered to clarify relations between MVCs that are caused by falling asleep and those that are not, and sleep problems or subjective sleepiness while driving under Japanese road conditions. We distributed questionnaires to drivers who visited a single driving license center in Tokyo, Japan. After excluding inexperienced drivers, 4097 drivers were included in the following analysis. MVCs were recorded over five years based on drivers' self-reports. Logistic regression analyses were used to examine MVC-associated factors. Results show that MVCs caused by falling asleep were associated with sleep duration of less than 6h, loud snoring or witnessed apnea, and sleepiness while driving. The MVCs not caused by falling asleep were associated with sleepiness while driving. This study revealed an association between MVCs and sleep problems or subjective sleepiness during driving among the respondents. In particular, sleepiness while driving was associated not only with MVCs caused by falling asleep but also with MVCs that were subjectively assessed as not being caused by falling asleep, suggesting that suppression of sleepiness while driving contributes to MVC prevention, irrespective of the occurrence of falling asleep.