Rising fuel prices reshape mobility decisions and can accelerate shifts from private to public transport. Yet, evidence on how these price dynamics affect rail accessibility at the local level remains limited. This paper investigates the relationship between fuel costs and spatial rail accessibility across Italian municipalities between 2016 and 2024. We develop an Italian Rail Accessibility Index (EN–3SFCA) that quantifies the potential accessibility of municipalities to the national rail network, accounting for both service supply and network-based travel time. Combining this index with a unique panel of fuel prices, socio-economic variables, and infrastructural controls, we estimate Two-Way Fixed Effects models and extend them with Instrumental Variable (IV) and Double Debiased Machine Learning (DML) estimators to address potential endogeneity between fuel costs and accessibility conditions. The results show a robust association between fuel prices and the rail accessibility index, indicating that changes in motoring costs modify the economic feasibility of accessing an otherwise fixed rail infrastructure, rather than the physical configuration of the network itself These findings highlight the structural role of rail infrastructure in buffering the effects of fuel price shocks and support the integration of accessibility measures into mobility and decarbonization policies.