COLUMBIA — Nobody knows when work will begin on the completion of the Mark Clark Expressway across Johns and James islands, despite the leap forward the project took Thursday.

What’s next

*Next steps for I-526

The S.C. Transportation Infrastructure Bank board still must approve the three-party contract.

The state’s Joint Bond Review Committee must approve the final $130 to $150 million.

Various agencies need to approve four environmental permits.

*No dates have been set for these steps, and the project may require other steps as well.

But it will be years.

The state Department of Transportation Commission voted unanimously in favor of a revised contract for the completion of Interstate 526 at a meeting Thursday. The vote marks the first concrete step forward for the long-stalled project since Charleston County Council voted to move ahead with it in December 2012.

But many steps remain for the project. The S.C. Transportation Infrastructure Bank board still must approve the three-party contract; the state’s Joint Bond Review Committee must approve the final $130 to $150 million; and various agencies need to approve four environmental permits.

Conservation groups have said they possibly will file lawsuits to attempt to stop the permits from being issued. Citizens could file lawsuits over compensation as well.

Local and state elected officials, and representatives from the DOT and Charleston County, all have said it likely will be years before any dirt is moved. Nobody publicly has estimated how many years.

But many project supporters said they felt optimistic after the commission’s vote.

Brad Taggart, a member of the local group Charlestonians for I-526, said he thought the contract approval marked “a huge step forward.” It appears the road will be built, he said. “The SCDOT was the last speed bump.”

The new contract, known as an intergovernmental agreement, for the $558 million project will give more control of building the road to Charleston County. That role usually is reserved for the DOT.

Commissioner Jim Rozier said the commission approved the plan because it made clear that the DOT would have no financial commitment to the project. The DOT also would be required to oversee and approve design and construction plans.

“We’re finally here,” said S.C. House Speaker Bobby Harrell, a proponent of the controversial project. “It’s time to build the road.” The DOT Wednesday added a presentation by Harrell to the agenda of a workshop before the commission’s regularly scheduled meeting.

I-526 proponent Bryan Derreberry, chief executive officer of the Charleston Metro Chamber of Commerce, and Coastal Conservation League Director Dana Beach, an opponent, also addressed the commission during that workshop.

Updating the three-party contract is the next required step for the project. In its initial $420 million contract, Charleston County was the project’s sponsor, the DOT was responsible for building the road, and the S.C. Transportation Infrastructure Bank was responsible for paying for it. But Charleston County wanted more control of building the road, and the price estimate had climbed to $558 million.

Harrell said the Infrastructure Bank board still must approve the revised contract. “But we don’t expect that to be a problem.”

Beach said after the meeting that he wasn’t surprised by the results, and that he didn’t come to Columbia thinking his pitch would get the commission to shoot down the contract. “But I wanted to get it on the record that they made a decision to invest in something that wasn’t important and not to invest in state and regional priorities.”

The completion of I-526 is not highly ranked on state and regional road priority lists, while the state’s road repair and construction needs are daunting, he said.

Ron Patton, a chief engineer for the DOT, told commissioners that he’s satisfied with the contract arrangement that DOT and Charleston County staffers have worked out. It addresses the DOT’s three major concerns, he said. It ensures that:

The DOT would have no funding commitment to the project.

Charleston County would develop the request for proposals for companies to design and build the road, but the DOT must approve of the document.

The DOT would hire the construction inspector for the project. The inspector would report only to the DOT, but Charleston County would pay the bill from project funds.

Charleston County Council Vice Chairman Elliott Summey also attended the meeting. He said he was “very satisfied” with the contract revisions that county and DOT staffers ironed out.

Now the county and the Infrastructure Bank will have to work out a policy on cost overruns, he said. But he doesn’t think there will be any cost overruns because the $558 million project estimate includes a 30 percent cost contingency on land and construction. And, he added, “the SIB never has not funded an overrun.”

He also said that the county would be responsible for handling compensation for property owners who live within 1,000 feet of the road.

The motion to approve the project in 2012 included an amendment, proposed by Councilwoman Anna Johnson, that the county would make “good faith efforts to evaluate and consider claims made by residents for compensation due to the impact of the Mark Clark Expressway on their property.” Many officials and county residents interpreted the amendment to mean property owners within 1,000 feet could be compensated for the drop in the value of their property.

Summey said he can’t address “mitigation and quality of life issues” yet because the path for the road is not yet certain. “Whatever is fair will be done,” he said, “but we can’t put the cart before the horse.”

Reach Diane Knich at 843-937-5491 or on Twitter at @dianeknich.