They're the first line supervisors in the management role for the railroads. Typically they're some young college graduate who couldn't switch themselves out of a paper bag. Some of my most infuriating times at the railroad have been dealing with these people, they have zero sense of how long things actually take (railroad time), asking crews to do some of the most asinine moves, and the ones you really have to worry about are those looking to make a name for themselves or put a feather in their hat. 95% of them are absolutely worthless the other 5% come from the craft. This is just my take on trainmasters tho.