What is the difference between "travel by train" and "travel by railway"? I would consider them synonymous.
Assuming you meant "travel by railway", yeah ... it sounds a bit strange to me, but the word "railway" is not really in my active vocabulary so I can't judge. I always say "train" or "train tracks" or whatever fits.
Why plural only?
Why can't it be Utasafiri kwa treni?
It should be accepted.
Also what's the difference between "kwa" and "na" . "Na boti" was apparently the right thing to say.