Regulations, the system of penalties, and police enforcement are key components in improving road safety. This article discusses the principles that law enforcement should adhere to in order to maximize its effectiveness, presenting empirical data from surveys conducted among the general population in Spain and the Dominican Republic on knowledge of traffic regulations, motivations for compliance and non-compliance, penalties, the perceived and actual likelihood of being sanctioned, and evaluations of the enforcement system. The evidence is compared with principles of learning and behavior—particularly those related to punishment—drawing conclusions about the common shortcomings of enforcement systems in many countries and the opportunities for improvement.