I don't know much about Atlanta, other than what I've read. I've never been there, though my impression of the place as a poorly-planned posterchild for suburban sprawl seems to be born out by the numbers; a city of a few hundred thousand in the middle of a multi-million-person metro area. The recent snowstorm and attendant traffic jam further confirms my impression.
Since I don't really have much insight on the situation, I'll just link to other sites that have spoken more authoritatively on the suburban sprawl roots of the problem. Matthew Yglesias gives a brief but clear description of Atlanta's urban planning shortcomings. Politico magazine gave a more in-depth treatment. And finally, CNN gave a scolding but relevant review of possible ways to avoid such problems in the future.