The introduction of public transport infrastructures is typically accompanied by political discourse expecting "shock effects" on the supply side to translate unconditionally into sustainable mobility practices on the demand side. This study examines how mobility practices have evolved in the wake of such a shock effect, focusing on the introduction of the Léman Express, a cross-border regional rail network that substantially enhanced public transport in the Greater Geneva. Drawing on two surveys conducted before (2018) and after (2022) the inauguration, we combine inductive Multiple Correspondence Analysis with Difference-inDifferences design and Propensity Score Matching to compare matched populations exposed and not exposed to the new infrastructure. We identify two latent dimensions structuring mobility practices in the regionenvironmental concern and valuation logicalong which the evolution of practices can be tracked while controlling for the confounding role of the COVID-19 pandemic. Our findings reveal that exposure to the Léman Express is associated with a partial attenuation of a general decline in sustainable mobility practices over the period, rather than with a positive shift. This attenuation is moreover narrow in scopeconcentrated on environmental concernand unevenly distributed across the population, remaining confined to urban, well-educated subgroups. By holding the behavioral, attitudinal, and practical aspects of mobility within a single analytical frame, this study contributes to an interdisciplinary dialogue between Transport Studies, Transit Oriented Development scholarship, and Social Practice Theories, and offers evidence on how mobility practices (do not) adapt when confronted with a major infrastructural change.