This Master Thesis aims to investigate the macroscopic effects of police enforcement on the improvement of road safety. For this analysis, a detailed and integrated database was developed, containing data on accidents, road traffic violations and socio-economic characteristics of Prefectures of Greece for the period 1998-2002. By the use of cluster analysis, four groups of Prefectures of Greece were identified. Using the non-linear Poisson regression model, statistical tests were performed and concluded in the statistically significant parameters, which influence the number of accidents in each group of Prefectures. The results demonstrate the importance of speed controls, alcohol tests, and enforcement of violations of priority and red traffic light. The enforcement effects varies depending on the type of road network (urban – rural) and the type of violation for each group of Prefectures.