Describe the suggestion
I suggest to change the movement system: If you are outside of a train, then you have to open the doors first (By right clicking it or something) and then, without any clicks, you could enter to it as in real life (So you don't right click the train, you just walk into it). Then if you are inside, you click on a seat, and the character sits on the seat you right clicked. If it's the seat of train driver, then the gui about speed, and other stuff shows up. It requires to change the hitboxes (Floor, walls or even stairs. With the stairs working in the trains, we could make double-deck trains, as @SebastianD334 metioned here #1050 ) to make it possible to move inside the train. About seats, modelers could name the seats for example like "SEAT_ID".

Applications of the suggestion
In my opinion, this suggestion will dramatically increase the immersion level, as moving in the train will be way more realistic.