^testarossa and Tuckerman, That's not the full story. There are indeed streams of money for transit expansion. Most obvious is MARTA - the recession was a huge blow to their funding source (1% sales tax), but they are now turning a profit. They were able to expand heavy rail multiple times over the last few decades, and recently added an
express bus route with traffic signal priority and queue jumping lanes. With Clayton County joining MARTA next year, there will be an additional source of revenue, with specific plans to build rail within ten years.
Then there's the Beltline. They have a Tax Allocation District (TAD) set up that will raise a lot of money for transit. There are currently thousands of apartments and a huge amount of business and office space under construction within the TAD, which will bring in a lot of revenue for transit.
In addition, any transit projects can and will leverage federal funding. The Streetcar is a great example. It didn't get any funding from MARTA, the Beltline, or the State of Georgia. It was mostly Federal and then some city, Central Atlanta Progress, etc. MARTA can leverage funds like this in the future, in fact it's assumed that for any major rail transit project in the US some of the funds will come from USDOT.
Of course it would help if the state actually supported transit and if congress was more supportive of transit, but there still are plenty of ways to get things done.