On January 1st, 1999, a prefix has been added to the registration number to distinguish locomotives based on type of activity to which they are assigned (followed by a 0 if the previous number had only 4 digits):
- 1: major routes
- 2: intercity
- 4: freight
- 5: regional express trains
- 6: infrastructure
- 7: responsible for the routing of empty equipment, under reparation or written off
- 8: Ile de France region