A brief review of the geographical and economic literature indicates that the current state of knowledge does not allow definitive conclusions about the effect of transport infrastructure – particularly high-speed rail – on regional development. Given this scientific uncertainty, territorial foresight is of strategic interest. This is why the method and results of a foresight study of planning stakes raised in Western France by the Brittany-Pays de la Loire High-speed line and related projects are presented from five scenarios by 2040.