Roads
For the national highways (within or outside town or city limits), contact the Direction Interdépartementale des Routes (DIR), the equivalent of a Road Authority.
For the departmental roads, contact the Departmental Councils (contact details for the relevant departments are available from local film commissions).
For the municipal roads (and all roads going through a town or city, except national highways), contact the mayors’ offices (contact details for the relevant departments are available from local film commissions).
Motorways
The motorways system is almost entirely managed and maintained by private companies.
First, contact the company to be sure the shoot is feasible, then submit your application to both the police department and the motorway maintenance company.
To know which motorway company to contact, check with Film France network.