Gov. Nathan Deal and top legislators have a plan to pay for the beleaguered toll road project along I-75 and I-575 in Cobb and Cherokee counties: lots of gas tax money.

The state Department of Transportation is not on board yet, and might have to decide on the expenditure. However, House Speaker David Ralston, R-Blue Ridge, said he hopes the $300 million that was in a budget plan passed by a House committee Thursday will make it into the final version of the budget.

The plan, which would offer big congestion savings to people who pay the toll, would put more gas taxes into one project than the state Department of Transportation's entire annual budget for all road widenings last year.

The project would build two optional, reversible toll lanes alongside I-75 from I-285 to I-575, and one reversible toll lane each along I-75 up to Hickory Grove Road and along I-575 up to Sixes Road.

The project was the state's maiden venture into privately financed toll roads, but last year, the DOT, at Deal's urging, canceled the bidding on it. Instead of private financing, which would have turned the toll road over to private companies for 60 or 70 years, the state is attempting to do the project with government funds. Deal had objected to restrictions on road-building that would have come with a private contract.

The new plan would add $300 million in gas tax money to fill the gap left by the defunct private investment.

"This is a promise kept by the governor," said a spokesman for Deal, Brian Robinson. "He laid this out in his State of the State address as a priority. He then set about fulfilling that promise ... and getting the money we need."

Transportation officials currently estimate the cost of the project at nearly $900 million.

The state already had $300 million set aside for it in gas taxes and borrowing, and had also lined up a federally sponsored loan of $270 million. So if all that were still available, that left a funding gap of about $300 million, which the new plan would fill.

But Rudy Bowen, chairman of the DOT board, said he had not discussed the new plan with the governor's office, and the DOT board would have to approve the funding package for the project. He took issue with using the original $300 million the state had set aside when it was a privately funded project.

"That original $300 million was for the [public-private partnership]," he said. "We killed that process."

DOT officials said they have been working on other options, including more borrowing against the expected toll revenue. They still hope to get the federally sponsored loan; U.S. Transportation Secretary Ray LaHood said Wednesday that the project was a good one and that Washington would re-evaluate the loan application in light of the project changes.

If it's built, the road will speed up commutes for people who pay the toll. But according to a state study, it won't do much for people in the regular lanes, and for some of them, it could even slow their commutes a tiny bit. That's because the toll lanes are reversible, so they only take cars off the regular lanes in one direction. The toll price, charged electronically, would rise and fall with congestion in the main lanes, aiming to always keep the toll lanes free-flowing.

It remains to be seen whether the new financial plan will pass the full Legislature after lawmakers learn more about the details. The plan would put a total of $500 million in gas tax money into one project. The state DOT's entire statewide road construction budget last year was about $722 million, with half of that just spent on repairs.

Ralston said the new plan was the right thing to do. "I think the significance and impact of this project is so substantial that the investment is wise," Ralston said. "We’re long overdue for improvements in that corridor, and I look forward to seeing that this gets in the final version of the budget."

The plan could take care of one major political headache, in the perennial contest between roads and mass transit. A regional transportation referendum scheduled for metro Atlanta this summer includes an expensive and controversial mass transit project near the I-75 corridor, but no comparable highway project.

When the state pulled the plug on the I-75 road project, a key supporter of the mass transit project, Cobb County Commission Chairman Tim Lee, backed off and called for gutting it in favor of the toll road.

Tad Leithead, chairman of the Atlanta Regional Commission and of a business district in the I-75 corridor, said, "Hey that's great!" when he heard about the latest plan.

"If the state has identified a method for funding this project outside the project list in the referendum, then the high-capacity project can remain on the project list," Leithead said. "I think that would be a win-win for all concerned."

The new piece of the funding puzzle, $300 million from gas tax money, was passed by the House Appropriations Committee on Thursday morning, buried deep in a budget document. It concerns gas tax money that already has other projects waiting for it, said House Transportation Committee Chairman Jay Roberts, R-Ocilla.

Staff writer Laura Diamond contributed to this article.

By the numbers

The total project cost could be short of $900 million. This is how a new plan breaks it down:

$300 million: gas tax money newly diverted by the Legislature

$270 million: a federally sponsored loan, approval pending

$200 million: gas tax money previously approved*

$100 million: bonds previously approved*

* DOT leaders say the old approvals are defunct.

Sources: Office of the Governor, state DOT, Georgia House of Representatives

Story so far

2005: The Georgia Department of Transportation signs its first partnership to develop toll lanes along I-75 and I-575. The original plan is to add eight lanes, but the estimates skyrocket from about $2 billion to $4 billion.

2009: DOT abandons partnership on the project, scales it back.

September 2011: The latest I-75/I-575 project -- with 29 miles of reversible toll lanes on I-75 and I-575 -- goes out to bid.

Oct. 1, 2011: An HOV lane on 16 miles of I-85 in Gwinnett and DeKalb counties becomes a toll lane, leading to an outcry from drivers facing longer wait times in the regular lanes.

Nov. 14, 2011: When The Atlanta Journal-Constitution asks the governor's office about a study that says the I-75/I-575 project would provide limited relief from congestion for most people, the governor's spokesman says the study raises "serious questions."

Dec. 14, 2011: The state DOT pulls the plug on the public-private project but says it will look at other ways to build it.

Feb. 2, 2012: A state budget plan that includes another $300 million in gas tax money for the I-75/I-575 project passes the House Appropriations Committee.