How anger, anxiety, and sleepiness shape everyday driving behaviour: A repeated-measures diary study with actigraphy

Introduction: Driver behavior is a leading contributor to road crashes. Emotions such as anger and anxiety, along with fatigue, are well-established risk factors for unsafe driving. However, most research examines these influences at a single time point and overlooks how traits and situational context may interact to shape behavior. Method: This study used a seven-day diary design with 35 licensed drivers (Mage = 44.25; SD = 15.11; 54 % women) to investigate how anger, anxiety, and fatigue relate to aberrant and positive driving behaviors across everyday trips. A secondary aim was to explore whether trait propensities for anger and anxiety interact with situational context to shape behavior. A total of 346 trips were recorded, capturing trip characteristics, emotional states, sleepiness (Karolinska Sleepiness Scale), and self-reported behaviors (Driver Behaviour Questionnaire). Sleep was measured via wrist-worn actigraphy. Results: Anger and anxiety were low but common, reported on 31 % and 48 % of trips, respectively. Generalized estimating equations showed that trait anxiety was associated with increased odds of experiencing both anxiety and anger. Passenger presence and congestion were also associated with experiencing anxiety, and anger-prone drivers were more likely to experience anxiety under high congestion. Higher congestion was associated with fewer aberrant behaviors, consistent with drivers adjusting to increased demand. However, this pattern was weaker among drivers with higher trait anxiety, who reported more violations, errors, and lapses, specifically under high congestion. A similar interaction emerged for trait anger and violations. Aggressive violations were associated with anger, and this association varied by level of sleepiness; with sleepiness weakening the anger-aggression relationship while strengthening the anxiety-aggression relationship. Positive behaviors were associated with longer preceding-night sleep and driving without passengers. Conclusions: These exploratory findings suggest that driving behavior may be conditional on the combination of who the driver is and the context in which they drive.