The next (possibly first) two or three digits of a vehicle's number indicate its class, in loose bands corresponding to the traction and power output of the stock:
A Class 22200, 195th in series, operating under TER bears the number 522395.
The final digits uniquely identify the engine within its class, but in the case of a three digit class number, the engine number may begin adding to the class number (for example, a Class 22200 may have a number beginning 222, 223 or 224).
Multiple units are numbered the same as locomotives, but prefixed by X for DMUs or Z for EMUs. Diesel shunters are prefixed Y. A now discontinued practice was to prefix the class number by the wheel arrangement.[2]
TGV numbering scheme
Each TGV trainset has its own number, found on the nose. Within the set, each vehicle is given its own number. The power cars are numbered by the standard locomotive numbering scheme, prefixed by TGV. The trailers are given a number which consists of the first two digits of the power car's number, followed by the number of the trailer in the set, and finishing with the number of the trainset, prefixed by TGVR or TGVZR, if powered.[2]
The SNCF adapted the classification system introduced by the Chemins de fer de Paris à Lyon et à la Méditerranée in 1925. This consisted of a numeric prefix derived from the axle (not wheel) arrangement of the locomotive, a letter for the class, and finally a number for the locomotive with the class. SNCF's adaptations included using the axle arrangement in full, and reversing the class letters of tank locomotives. For example, the SNCF used 040.A., and 242.TA. where the PLM used 4.A., and 242.AT.
Class letters A-N were used for existing designs, letters P onwards for SNCF designs. Others railways' designs taken over after World War II were usually given the letter U (American), W (British), X, Y, or Z (German).
Where locomotives were upgraded or rebuilt, the class letter changed, but not the number. While the Region Nord renumbered all their classes from 1, the remaining 4 regions re-used the last three digits of the old number in the new number.
As there were more classes that available letters of the alphabet, the axle arrangement was prefixed with a digit indicating the owning region: 1 Est (former Est and AL lines), 2 Nord 3 Ouest (former État lines) 4 Sud-Ouest (former Paris-Orleans and Midi lines) 5 Sud-Est (former PLM lines). Region 5 was later split in two, with the southern part becoming 6 Mediterranée
Locomotives transferred from one region to another could change their class letter and numeric suffix.
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