Since in Europe we tend not to rely on exactly 2 different type of locomotives, we kinda need the extra numbers to segregate the different series.
Have a seizure at the wonderfully French 6 numbers ID system. The first is activity (Freight, long haul pax, regional pax, maintenance...), the next 3 are class type, the last 2 loc (or EMU/DMU) ID (if you need more than 100 just bump that 4th number up -or down if bumping it up would push it in another sub-class).
Pic related for instance shows the BB115042 (BB layout, 1 for mainline pax, class 15000, number 42) and the BB122339 (mainline pax, 22200 class, number 139).
I consider this chaotic evil.