This program of research examines the relationship between young drivers' views of police legitimacy and their driving intentions and behaviours on the road. Police legitimacy refers to the public's perception of the police as a trustworthy, fair and effective authority whose actions are morally aligned with societal values (Tankebe et al., 2016). In the context of road safety, this program of research aims to determine if the public views police as legitimate and are more likely to comply with road rules, thus reducing risky driving behaviours that often lead to crashes, and enhancing overall road safety. The central aim of this research is to explore how these views of police legitimacy affect young driver' compliance with road rules and their willingness to engage in risky driving behaviours, contributing to their over-representation in serious and fatal crashes. This research employs a mixed-methods approach, incorporating longitudinal, experimental, and qualitative methodologies to provide a comprehensive exploration and understanding of factors that have not yet been considered in the research that may influence young driver behaviour and overall safety on the roads. The primary objectives of this research are fourfold. First, I assessed the immediate impact of a police-led school-based road safety education program (the LAW program) on young drivers' views of police legitimacy and self-reported driving behaviour. Second, I investigated whether the presence of uniformed police officers during educational road safety programs, such as the LAW program, significantly influences young drivers' views of police legitimacy when compared with plain-clothed officers. Third, I developed and evaluated a co-designed digital road safety intervention aimed at reinforcing safe driving behaviours and improving views of police legitimacy. Finally, I examined changes in young drivers' views of police legitimacy and self-reported traffic offences over time to understand the longer-term effects of the police-led road safety program and the co-designed digital intervention. This program of research utilises a combination of quantitative and qualitative methods. A quasi-longitudinal design was employed to assess changes in young drivers' views of police legitimacy and their self-reported traffic offences over time. This required surveys to be administered at multiple time points to capture the evolution of these views and behaviours. An experimental trial evaluated the impact of police uniforms on young drivers' views of police legitimacy. Young drivers attended a police-led road safety program delivered by the same police officers in either uniform or plain clothes, and their views of police legitimacy and driving intentions were measured. A digital road safety intervention was developed using a collaborative design process involving both road safety experts and young drivers. The intervention aimed to deliver engaging and effective, evidence-based road safety messages tailored to the target audience. The intervention was approximately 4 minutes long. The effectiveness of the digital intervention was assessed through follow-up surveys conducted three months post-intervention delivery to examine any changes in driving behaviours and views of police legitimacy between those who received the intervention and a comparison group. The key findings of this program of research are significant, both theoretically and practically. Participation in the LAW program led to improvements in young drivers' views of police legitimacy, which were significantly associated with lower intentions to offend. The presence of uniformed police officers during the LAW program had a greater positive impact on young drivers' views of police legitimacy and intentions to comply with traffic laws compared to when the same officers presented the program in plain clothes. While the co-designed digital intervention was well-received at the design stage and had input from both young drivers and road safety experts, it did not lead to significant changes in self-reported driving behaviours and offending. However, longitudinally, views of police legitimacy remained a significant predictor of young driver behaviours. The quasi-longitudinal study revealed that initial positive views of police legitimacy following the LAW program decayed over time, highlighting the need for sustained positive interactions between police and young drivers to maintain these views. [...]