Aggressive drivers pose a significant road safety threat to themselves and other road users. Therefore, understanding the relationships between certain cognitive processes and increased frequency of aggression has the potential to reduce road trauma through intervention. This study examined the relationships between anger rumination and forgiveness with trait driving anger and aggressive driving. These factors have previously been individually identified as predictors of aggression; but have yet to be considered simultaneously, despite recognised association between forgiveness and rumination tendencies outside of road safety research. Aggressive driving was measured across three facets of behaviour: verbal aggression, physical aggression, and use of the vehicle to display anger. Adaptive constructive responses to driving anger were also considered. Five hundred and one drivers (mean age = 43.7; SD = 17.7; men = 53.8%) completed an online questionnaire seeking information on these factors. Structural equation modelling showed that, after controlling for gender, 62% of the variance in aggressive driving was explained by a combination of trait driving anger, more frequent rumination and lower levels of forgiveness. Specifically, lower levels of forgiveness predicted more anger rumination (accounting for 49% of the variance), and the relationship between anger rumination and aggression was fully mediated by trait driving anger. A second model demonstrated that 17% of the variance in adaptive constructive responses to anger could be explained by higher levels of forgiveness, lower rumination and driving anger. Efforts to improve driver behaviour need to focus primarily on the reduction of driving anger. This could be achieved by reducing rumination through the promotion of forgiveness for the behaviour of other drivers.