I'm an experienced native speaking ESL teacher looking for a concise way to explain how to choose between "ride a bus", "take a bus" and "be-verb on a bus". I know a clearly correct explanation when I hear one, and I can't say I've heard one on this issue, so my initial fear is the decision tree will turn out to be a complex one. Please prove me wrong.
To keep answers and comments as focused as possible, I'm NOT interested in rules about "ride the bus", nor "drive a bus", nor about any other means of transportation other than bus (if the rules we come up with apply more broadly, that's gravy, but they're not my objective here).
Searching the Internet reveals mostly opinions that they're all freely interchangeable, which is not the case.
More insightful people online suggest a nuance where "take" is more about the mode of transportation, while "ride" refers to the ride itself. This feels like it's on the right track, but it's not well-defined enough to enable an ESL student to confidently choose between them.
It seems to me that "ride a bus" and "be-verb on a bus" are closer in meaning to each other than "take a bus". If they mean nearly the same thing, then what governs the choice of one over the other?
In the simplest examples, with no context, if someone says, "I'm riding a bus", I assume they're on the bus right now, but if, with no context, someone says, "I'm taking a bus", I assume they haven't gotten on yet. So does "take a bus" have some future-ish aspect to it? Or does "take a bus" mean "get on a bus"? Neither of those seem right, but I'm willing to entertain them.
In many contexts, two or all three of them will be correct, so most of what I'm looking for will be rules for which is/are the most natural in that context.
As I alluded to above, if you can demonstrate that the answer too complex a thing to explain clearly enough to be useful to an ESL student, I'll accept that as an answer, and at least I'll be able to confidently say that it's a tough question.
And that's as far as I've gotten on my own.