What does the 'reverser' switch in the cab do?

https://preview.redd.it/vvvmwwzkzqbe1.png?width=245&format=png&auto=webp&s=34adcffb7f9d4da66b3a42e8740c5b546fa6baec

This reverser switch in the cab (not the TBC): what are the settings, and what do each of them do? I'm most curious about what happens if you set it in reverse: does the train drive backwards like a car reverses?