prepositions - What/Which train are you going on/by?

What is the difference between the following interrogative structures?

• What train are you going on/by?





• Which train are you going on/by?

And which of the prepositions, given at the end of both structures, would be appropriate?

Answer

Practically speaking, they both mean the same thing. Perhaps if there were a number of trains at a station, someone would say "which" train, but "what" is also acceptable.

In terms of the preposition, I have heard both prepositions used.

Personally, I would say either "Which train are you taking?" or "Which train are you on?"