I would use "on".
I have a question as to the usage of 'by'.
Is it possible to say "They go to Kyoto by these buses" in a situation where there are several buses in front of us?
Should it be " [...] on these buses"?
If they are not yet on the buses, should "on" still be used?
We may say "by bus" or "on the bus" but not "by the bus".
Is it correct?