The Main Clause
All five (six actually) constructions clearly communicate the main idea:
The train was delayed.
The Relative Clause
All five relative clause constructions also clearly communicate I was traveling on the train that was delayed:
1) by which I went:
Train is modified by I went, using which as the object of the prepositional phrase:
- When we use whom or which the preposition sometimes comes at the beginning of the clause:
You were talking about a book. I haven’t read it. >>>... I haven’t read the book about which you were talking.
This is a perfectly legitimate construction, even though it can sound awkward.
2) by which I travelled
Train is modified by I traveled, using which as the object of the prepositional phrase. Again, a perfectly legitimate construction, replacing went with the equivalent verb travelled.
3) which I went by
Train is modified by I went, using which as the object of the prepositional phrase, with the preposition following the verb phrase:
- as object of a preposition. When the relative pronoun is the object of
a preposition we usually put the preposition after the verb ...
You were talking about a book. I haven’t read it. >>> I haven’t
read the book which you were talking about.
It is perfectly acceptable to put the preposition after the verb in a relative clause.
4) which I travelled by
Train is modified by I traveled, using which as the object of the prepositional phrase, replacing went with the equivalent verb travelled.
5a) I travelled on
Train is modified by I traveled, reducing which from the prepositional phrase:
- When the relative pronoun is the object of a preposition we usually leave it out:
That’s the house my parents live in.
The missing relative pronoun is clearly understood.
5b) I was on
Train is modified by I was, reducing which from the prepositional phrase, replacing travelled with the verb was. I went by would work but it might create a little confusion between walking by the train (local), and traveling by the train (instrumental).
The Prepositions
Although by would not work with the verb was, both by and on work just fine with both travelled and went.