Spatial planning is always potentially conflictual, especially the planning of transport infrastructure. Conflict resolution is therefore an important segment of theoretical discussions, which usually focus on rational and participatory approaches. While the legitimacy of technical rationality is based on the objectivity of scientific decision-making, the participatory approach focuses primarily on achieving legitimacy through public participation and deliberation. In practice, both approaches have shortcomings – the former is criticized for its ignorance of the social context, while the latter is criticized for its utopian principles of truthfulness, correctness, and sincerity, on which deliberation is based. In Slovenia, studies that examine actual conflict resolution processes without assessing the appropriateness of planning approaches are rare or practically non-existent. This study, addressing conflicts in transport infrastructure implementation, focused on two case studies, the planning of the highway through Trebnje and the planning of the motorway between Šentrupert and Velenje. We investigated the roles of involved actors, the causes of conflicts, arguments, and approaches to conflict resolution. The aim of the research was to determine how to achieve legitimacy in practice, which is always potentially conflictual. We used the following qualitative research methods: analysis of documents and newspaper articles, and analysis of interviews. The results were interpreted using the complexity theory and the actor-network theory, which emphasize the dynamic nature of decision-making. Research has shown that conflict resolution is influenced by various social contextual factors, which is why the conditions for achieving legitimacy change. Decision-making therefore requires continuous deliberation between involved actors and the adaptability of decision-making processes. In addition, decisions must always be based on the broadest possible social and scientific consensus. Deliberation between territorial units is also important in spatial planning of transport infrastructure, which is problematic in Slovenia due to the absence of a regional administrative level. Although this study is limited to transport infrastructure in Slovenia, its methodology can also be used to study other spatial conflicts, including those on an international level.