rather = prefer, here. As in the choice between self driving cars and buses.

I was also confused, and I'm a native speaker. Understanding that "rather" means "prefer" is obvious.

The sentence could be read as "I prefer to be on the road with a bus since I think it's safer". Or it could be "choosing what's most dangerous, I'd rather say it's a bus".

It's also not clear what the perspective of the speaker is. It might be that a bus is safer for the rider, but more dangerous for cars around it. So would he rather be on board a bus, or rather on the road with a bus?

I have no idea how you could get that second interpretation from what he said. And the perspective is clearly inherited from the parent comment, who didn't mention being "on board" a bus, just "on the road with" a bus.

No ambiguity in that comment that I can see.

EDIT: I guess the use of rather in this context could be a colloquialism?

You knew what he/she was trying to say...

Personally, I don't and I'm a native English speaker. I doubt many who weren't would have any chance of deciphering the meaning here either.

I see this usage fairly regularly. I'm not 100% certain of this, but I think it might be more common in Britain than America.

It's just an ellipsis. Or, as my first Google hit said:

"the omission from speech or writing of a word or words that are superfluous or able to be understood from contextual clues."

So: I would rather [have] a bus any day.

Is "I would rather you did..." odd too? Not a native speaker here :)

> Personally, I don't

That's more on you than the OP. It's hardly an unknown phrasing.

Actually, I didn't. It's an odd word choice, and 'prefer' would have made more sense. Rather is typically used in conjunction with another verb, while prefer isn't.