Aggressive driving is acknowledged as a contributor to motor vehicle crashes. This study explored a theoretical model of aggressive expression and crash-related outcomes using self-report data collected, using an online questionnaire, from drivers in the United Kingdom and the Republic of Ireland. The proposed model tested whether the personality traits of boredom proneness, sensation seeking, and impulsivity, coupled with trait driving anger, predicted aggressive driving; and whether aggressive driving predicted crash-related outcomes (loss of concentration and control, near misses, and moving violations). The structural model was confirmed, with aggressive expressions of anger being found to mediate the relationships driving anger and impulsivity had with the crash-related outcomes. Multigroup invariance analysis showed that the model remained invariant across drivers from the United Kingdom and Ireland, suggesting that the contributing factors for aggressive expression and crash involvement are similar across both countries. When self-reported crash-related conditions were compared between drivers in the United Kingdom and Ireland, drivers in the United Kingdom reported more aggressive driving, more minor crashes, more incidents of road rage, and more frequent losses of concentration and vehicle control.