ERTMS implementation in France =>ERTMS for on board + national trackside). Problem: hard to evaluate the whole system regarding safety requirements. Ordinary method of railway standards comparison => Experienced experts to compare the detail entries of each rule. Weakness: Low-productivity. Solution: Set up formal specifications of ERTMS and local system to assess the safety of an ERTMS solution on a given french system. Railway interlocking system is a crucial link of local system. The methodology of establishing the formal petri net model of French railway interlocking is the main focus of the work.