I use my open MA900 for walks, hikes and even public transport travel and any other travel. Either these isolate more than they're given credit to [unlikely], my local public transport does not require that much isolation or open headphones are vastly underrated for such purposes.
I have the K612 and if it was easier to drive, I'd give it a shot for that as well...
I don't listen too loud either, I have to listen about 1 - 3db louder than indoor, but that is still much less loudness than what my friends listen at... Seriously people just don't care or my hearing is exceptional.
/shrug, to each their own. Also, an airplane is quite a bit louder than a bus/train as far as noise level goes, especially if you end up right next to the engine.