To do this glitch it's easy just spawn into service turn on the train but don't touch any thing and what I mean by that is don't open any doors. The service is going to ask you to take over just say yes and take the whole journey to the last stop. Once at the last stop take over the service and it should end and complete
You can do that even quicker and easier by just spawning on foot at the final station, jump in and take over when the train pulls in. But then, why would someone want to do that... Isn't TSW about driving trains?
All I do is drive trains LOL and yes that is another way you can do that. I don't see no helpful for reason why someone would do it but I guess if they want to know now they can haha