If the transportation tax is approved in some Georgia regions and defeated in others, it will only be enforced in the counties that vote yes on Tuesday.
The ballot initiative has drawn attention because of its occurrence in staunchly conservative state.
But it has split traditional alliances in both the Democratic and Republican parties. Business groups who normally endorse GOP candidates have said they support the proposal, while Tea Party groups have rallied against the mere suggestion of a tax increase.
On the Democratic side, Atlanta Mayor Kasim Reed, who is a frequent surrogate for President Obama's reelection campaign, has campaigned furiously for the transportation funding. He has been opposed, however, by NAACP groups in the Atlanta area who have argued that the measure does not include enough spending in traditionally African-American areas.
Pre-election polls showed the transportation tax could be headed for a possible defeat, but supporters have predicted a narrow victory for the measure, at least in the metro Atlanta area.
Polls in Georgia are scheduled to close at 7 p.m.