Hi! I grew up in Baltimore. I miss it!
Obviously, you're too nice of a person to just march up to her house and tell her you've had it. It might be tim e to tart dropping some pointed hints. For instance, make sure you get gas when she's in the car--as you're pulling into the station, say "WOW! Gas sure has gotten exensive!" Then, *every time* you fill up, make a point to say how much it cost the fill the tank "Man, it was 24.57 to fill the tank! I must have been REALLy empty"... or "great, it only cost me 22.87 today!"
You might also try taking a day off every once in a while.... "oh, thursday i'm going to <insert lie>, so I can't take you to work. I hope this is enough notice for you to find a ride."
Or you could just got throttle her.