I realize a lot of questions have been asked about buses here. While the thing with the preposition usage was resolved for me a long time ago, the usage of the articles is still confusing me.
For example, which article would be more appropriate, if you were traveling in a vehicle and your phone rang and you wanted to avoid a conversation:
"I can't talk. I'm on a / the bus (in a / the car, on a / the train) right now. I'll call you back later."
My logic is:
In a situation when we're not talking about the specific bus/car etc. and just stating the fact that we're traveling in a vehicle, the indefinite article should be used.
So I would use "a". However, Google gives plenty of examples of both "a" and "the" used in similar situations. "The" seems to prevail, though.
Can you please explain the difference between "a" and "the" in these phrases?