The Atlanta Business Chronicle has a good rundown on the politics of funding this issue:
After much debate, state lawmakers appear more willing to move forward with a proposed regional penny sales tax during the 2008 legislative session that could raise billions of dollars to combat congestion in Atlanta.
At the same time, they are expected to abandon a proposed 1 percent state sales tax for transportation projects in favor of replacing the 7.5 cents-per-gallon state gas tax with an extra 0.5 percent state sales tax.
That would bring the statewide sales tax to 4.5 percent. The total rate in the city of Atlanta would rise to 8.5 percent. ...
How long the tax will run (likely five to 30 years), who will control the funding (the state, the ARC or some new entity) and what sort of projects can be funded (a percentage for local roads, highways and transit, perhaps) should be answered when the study committee releases its final report near the end of December, sources said.