Do you think it is a regional difference of usage? Os is it a matter of idiolect?
Some speakers of English make a further distinction for public modes of transportation, using in when the carrier is stationary and on when it is in motion.
My wife stayed in/on the bus while I got out at the rest stop.
The passengers sat in/on the plane awaiting takeoff.
Hi, I think that there's a lot of truth in this comment. It seems to me to be idiomatic, and not just regional, but perhaps other people may have a different opinion. Because it's idiomatic, you have to be careful about over-generalizing and making a 'rule'.
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