Before data collection and analysis can start, it is necessary to consider the question of which road safety indicators are considered relevant. Indicators can be used in policy making, for progress monitoring and for explaining developments, particularly in relation to the policy conducted. Good data are indispensable for this. When data are not good, erroneous decisions are possible. Improving road safety is a social issue, and society cannot afford to let dilettantes take erroneous decisions based on false data leading to unnecessary road casualties. In addition to their use in road safety policies, good data axe of extreme importance for research.