Abstract : Road safety is a key dimension of road planning. This thesis analyses the role of road safety in the planning decisions of the local public administration, in light of the transfer of national roads from the central State to the Départements in the second decentralisation and the restructuring of the DDE. Road safety is usually drafted as a technical objective in French research, which analyses it only according to infrastructure and planning. In our approach we also interrogate it from the point view of values - hence our interviews. This ethics-based approach is central to our research where we apply the model of the Action to the Value developed by Martouzet (2002). We demonstrate an evolution in attitudes to road safety in road planning following the restructuring. The decentralisation ended the DDE's monopoly of infrastructure expertise, renewing the role of the Départements which have become the main administrators of roads. The values and practices of the local authorities, and consequently of the State, evolves. The Département supplants the action of the DDE both combining the technical view of the road of the DDE and the urban questions of the Communes. The DDE and the Département have different conceptual approaches and these approaches continue to evolve dynamically, specifically regarding the emphasis on ethics in road safety.