If you let the Master's Army destroy Necropolis, a ghoul refugee who survived the invasion can be found hiding behind a bookcase with dialogue talking about the invasion, while also mentioning that the attacking super mutants had "some steam trucks". These steam trucks are the only working mechanically propelled vehicles mentioned in the game, and are only mentioned in this Fallout game.

In the eighth installment of the Fallout Bible, Fallout 2 developer Chris Avellone revealed that steam trucks were planned for Fallout, but they were only mentioned in passing for "art reasons and gameplay reasons" and that it may have been an "ugly-looking vehicle".
Contributed by MehDeletingLater