OK, time for a post with too much analysis...
Daria's 16, but we've never seen her -near- driving a car. She's caught rides with Trent or taken a cab, but never driven on the show. Could she have failed her driver's exam? Notice:
In "Esteemsters", she is talking to Helen and Jake about trust, and she asks to borrow either car. They immediately say "No."
In "Quinn The Brain," when Helen tapes Quinn's paper to the fridge, there's also a DMV violation there. But Quinn's only 14 1/2, she doesn't even have her learner's permit (College Bored). So it's not Quinn's, and Helen and Jake wouldn't put their own ticket on the fridge. Maybe that's why Daria doesn't have her own car yet: She got a ticket, and her parents don't "trust" her enough to give her the keys.
Of course, anything I've just said is subject to being horribly wrong... What do you guys think?
Chris Majors