Traffic laws attempt to improve driving standards by defining as illegal those types of behaviour which are held to be unduly risky, such as drink-driving or driving too fast. These laws are only effective if they are obeyed, but drivers frequently violate traffic laws without being caught. The likelihood of an offender being caught depends on the level of enforcement of these laws by human policing and increasingly by automatic equipment such as speed cameras. This report presents the results of a review of the relevant technical literature that was undertaken by TRL on behalf of Transport for London (TfL) to investigate 'How Methods and Levels of Policing Affect Road Casualty Rates'. The main aims of the review were: (a) to evaluate the findings from existing literature in order to determine whether increasing the level of traffic policing is likely to reduce the number of casualties in road accidents and (b) to summarise the main pieces of work and draw conclusions, including any quantitative relationships between the level of enforcement and the numbers of accidents and casualties. Overall, the literature showed that increased enforcement can lead to significant improvements in road safety. However, determining the precise relationships between levels of policing and casualty rates is problematic on the basis of the available literature. Detailed results are presented along with a brief proposal for a future research project to investigate the influence of levels of traffic policing on accidents and casualty rates.