— The state Department of Transportation and environmental groups said Thursday that they have settled a lawsuit holding up completion of the N.C. Highway 540 toll road in southern Wake County.

The agreement between the DOT and Sound Rivers Inc., the Center for Biological Diversity and Clean Air Carolina means the state can proceed with final permitting and project financing for the highway, known as the Triangle Expressway Southeast Extension.

Construction on the southeastern portion of N.C. 540 has been held up for years by environmental concerns, including an endangered mussel that forced state transportation officials to look at various alternative routes.

"This agreement is a win for North Carolina," Transportation Secretary Jim Trogdon said in a statement. "Instead of fighting in court, we negotiated a settlement that saves time and money while it protects and preserves some of this region’s most beautiful natural areas."

The agreement, which will be implemented during the next several years, includes the following provisions:

The DOT will take steps to reduce emissions from construction equipment, conduct greenhouse gas analyses as part of major project studies in North Carolina and focus on strategies and tools to reduce vehicle miles traveled and vehicular emissions across the state.

The agency will help enhance the water quality of critical streams and rivers in the project area by implementing additional protections, providing more stream mitigation and restoration, conducting research and developing new stormwater design guidelines. The department also will help Johnston County improve its stormwater management program.

The DOT will set aside funds to assist in Wake County’s goals to preserve open space for the benefit of the community.

The department will provide environmental work to protect streams, restore wildlife habitat and provide a lifeline for some of North Carolina’s rarest and most endangered aquatic species.

"This unprecedented agreement will be a game-changer for many of the most important environmental issues in our state," Kym Hunter, senior attorney with the Southern Environmental Law Center, which represented the three conservation groups, said in a statement. "This agreement sets in place critical protections for the Neuse River watershed, preserves beautiful open space in Wake County, provides a lifeline for some of the state’s rarest and most endangered aquatic species and creates important new mechanisms for combating climate change."

The settlement means that three environmental groups will end a federal lawsuit filed last year and claims in the North Carolina Office of Administrative Hearings filed early this year related to the environmental process and impacts of the construction of N.C. 540. In addition to the DOT, the Federal Highway Administration, the U.S. Fish and Wildlife Service and the National Marine Fisheries Service were defendants in the federal lawsuit and the state Division of Water Resources was a defendant in the state action.

The state has already awarded contracts to build the six-lane highway from east of Pierce Olive Road, near Holly Springs, to east of U.S. Highway 401 and from there to Interstate 40.

A third contract to design and build a segment of the highway between the N.C. Highway 55 Bypass in Apex and Pierce Olive Road is expected to be awarded later this year.

Construction could begin late this year, and the project is expected to open to traffic in 2023, officials said.

Work on the stretch between I-40 and U.S. Highway 264 in Knightdale wouldn't start until 2027, officials said last year.