Interesting that they're that low of a wattage. The equivalent wattage used in traffic signals would be 60-69w for the 8" lights and 116-135w for the 12" lights.
The general railway signalling (not crossing, but the signals along the track) works with very narrow beam optics, because the system should prevent the train driver to misinterpret the signals for adjacent track as "his" (in case of failures or some obstructions,...), that uses to be very fatal.
Because of the narrow beam, the required power is quite low.
In fact this need for precise focus is, why the bulbs are of low voltage filaments in the first place (so the filament spiral is very compact), as the signalling power uses to be quite standard mains voltage (to eliminate voltage drops due to the long wires to the supply points along the tracks). The transformers even use to have multiple voltage taps, to allow adjustment for the specific voltage drop at the given place and to keep the light output parameters in the tight tolerances the system requires (again to prevent train driver confusions)
And for logistic reasons, the crossings use the same bulbs (and related transformers - as in most places only the bulb) as used in general signalling, so the low voltage low power as well.
