Two staunch opponents of a proposed 1-cent sales tax for transportation announced a "Plan B" Friday if voters defeat the tax in Tuesday's primary.

The plan would include a single state motor fuel tax dedicated to transportation funding, local control over MARTA and public elections for all members of the state Department of Transportation governing board.

The unlikely alliance of the Georgia Sierra Club and the Georgia Tea Party Patriots have surprised even the groups' organizers, who announced the plan at a press conference at the Capitol — home base to one of the sales tax's biggest proponents, Gov. Nathan Deal.

At stake is a binding vote with billions of dollars worth of regional transportation projects across Georgia. Voters in each of the state's 12 regions will decide whether to approve the sales tax to pay for the projects. In the metro Atlanta region, the tax is projected to raise an estimated $7.2 billion over 10 years.