Résumé: This work estimates the impact of the 2018 French national railway strike (April to June) on the inter-city ridesharing supply and demand. We collected daily trip-level data from the API of BlaBlaCar, the largest inter-city ridesharing platform in Europe. On an average strike day, bookings increased by 26% while supply increased by 7% during the strike period. Total transaction value increased by 24%. Shorter routes had the largest increase. Furthermore, the recommended price proposed but not enforced by BlaBlaCar was sufficient to stabilize the price proposed by the driver close to the recommended level, even during the demand peak. Our result shows that inter-city ridesharing is a flexible and effective substitute during train supply shortages. We argue that policymakers should integrate ridesharing into transportation planning.