It was to answer this hypothetical question that a mock trial involving law students students from the Lyon Catholic University (UCLy) was held at the end of June. While the proliferation of the autonomous car could reduce the number of road accidents by up to 90%, it is unlikely to eradicate them completely. However, if the driver is no longer a human, how is responsibility established? At the end of this unique experiment, where there was an exchange of views between the City of Lyon, the insurer and the administrative tribunal, it was the local authority that was eventually found liable, because the tribunal considered it to be responsible for the faulty vehicle guidance beacons. Underlying this rather ordinary case are complex questions that highlight the role of infrastructure in the deployment of autonomous vehicles.