The Léman Express (LEx) is Europe's largest cross-border rail network. As the backbone of public transportation that connects Geneva with its French suburbs, the LEx should contribute to increasing sustainable mobility and to achieving the 2050 carbon neutrality objective. Accompanying measures such as new bus routes and tramways connected to LEx stations as well as bicycle lines, park and ride, and pedestrian facilities should be implemented to ensure that LEx achieves its full impact on the modal shift and active mobility. However, the findings in this study demonstrate that more than half of the LEx's accompanying measures are overdue; planning quality, national co-funding, and municipal support are key factors for reducing delays in their implementation. Notably, these empirical findings hold across the Greater Geneva area despite the institutional peculiarities of the Swiss and French political and administrative systems. This case study adds to the literature regarding European border studies by analysing the consequences of a cross-border environment on territorially bounded projects.