Are you planning a project by the boundary of a plot of land belonging to the railways?
You could need authorisation, an encroachment permit (permission de voirie) or your project could be prohibited.
Legal basis for the encroachment permit (1).
Installations by third parties for which an encroachment permit is needed, on or by the boundary of plots of land belonging to the railways (2):
Prescriptions for the development encroachment permit (3)
How to obtain encroachment permits (4)
Installations in need of direct authorisation from the CFL (5)
Safety Management System (SMS) (7)
Preliminary studies (8)
Construction supervision (9)
Cadastral limits to railway land (10)