In this research, the effect of the intensification of police enforcement on the number of road accidents and related fatalities at national and regional level is investigated, focusing on two most important infringements: speeding and drinking-and-driving. Distributional assumptions of the Poisson-family are considered for the counts of road accidents and fatalities of the various regions of Greece. A multilevel analysis technique is then applied to investigate the effect of the intensification of enforcement on the reduction of road accidents in different regions of Greece. Multivariate multilevel models are developed, in order to assess the combined effects of police enforcement in different regions and for different road safety outcomes (accidents with casualties and fatalities), and to quantify these effects. Results show a significant overall effect of enforcement on both road accidents and fatalities. As regards the regional variation of the effect, which results from different levels of intensified police enforcement per region, a significant difference between accidents and fatalities is identified. In particular, the regional variation of the effect of enforcement on accidents is highly significant, whereas no significant regional variation of the effect on fatalities is identified. The combination of the model results with additional behavioural data led to the conclusion that enforcement intensification has a direct impact on the improvement of driver behaviour and attitude and subsequently on the reduction of road accident and fatalities.