I have a car, but also try as much as I can to take Metro or the bus. If I took public transit and a friend had a car, I wouldn’t expect them to be my ride home. If they offered I’d be grateful and take them up on it, but wouldn’t begrudge them if they didn’t offer.

I’ve certainly given people rides when it’s out of the way for me, but I’ve never felt a weird sense of obligation to do that, and unless we talk about it beforehand I assume people have figured out their transportation already. If for whatever reason someone can’t get home safely, or there’s a significant Metro slowdown, I’d definitely take someone back in those cases.

Ultimately it’s up to you, and unless there’s a safety issue I wouldn’t expect other people with cars to go out of their way to take me home.