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.
If only Microsoft required a second prossesor like some sort of module just for encrypting and decrypting things without using additional CPU cycles... What if we also stored the encryption keys on that module so we could trust that platform...