Why plural only?
Why can't it be Utasafiri kwa treni?
It should be accepted.
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.
Also what's the difference between "kwa" and "na" . "Na boti" was apparently the right thing to say.
Railway is British. Railroad is American. You could compromise and say by rail.
Two once great nations still divided by a common language!
Since you can also be singular Utasafiri is not a TYPO