Incumbent actors, guided search paths, and landmark projects in infra-system transitions: Re-thinking Strategic Niche Management with a case study of French tramway diffusion (1971–2016)

International audienceThis paper concerns the emergence and diffusion of radical innovations in the context of sustainability transitions. We confront the typical understanding in the Strategic Niche Management framework with an in-depth longitudinal case study of French modem tramways (1971-2016), which represents a particular technology class: local infrastructure systems. The case confirms the relevance of existing SNM-concepts, but also points to three pattern deviations: 1) incumbent actors from neighbouring regimes can play a leading role in the development of radical alternatives, 2) the early formulation of highly specific visions can effectively guide search paths (as opposed to a usual prescription about more open-ended approaches to foster innovative variety creation), and 3) particularly influential projects (which we call 'landmark projects') can decisively accelerate innovation developments. Exploring a greater variety of diffusion and transition patterns (based on temporal interactions of causal mechanisms and varying roles played by different actors) is a fruitful way forward for sustainability transitions research