Actually if I am vaccinated (which I am) and am myself masked with a good quality mask (not some piece of rag around my nose and mouth) and sitting next to someone in a plane for a few hours would not really bother me much.
Since the collection of virons is cumulative, is it better to get to your destination quickly while well protected knowing you are in a risky environment than being in an environment which feels less risky for days while letting ones guard down a bit because it feels less risky?
Of course, being vaccinated, it would not bother me to be in the train environment either, even for days, while adequately protected. Just a week back I was in a pretty crowded train for an hour, where they actually enforced mask wearing quite strictly. And it was fine, in a place like Orlando, which according to some is borderline Armageddon territory as far as COVID goes.