In the US I can comfirm both GE (freight and passenger) and siemens passenger locomotives run Linux. Some passenger trainsets/cars still run embedded XP.

Pretty much all locomotives running out there today have a plethora of computers for managing fuel economy, brakes, and positive train control (rules compliance). Fun fact: the union pacific's 4104 'big boy' steam engine was fitted with wabtec's I-ETMS PTC which is powered by Linux so there's literally a steam powered locomotive running Linux.