Work is set to begin this fall along a 2½-mile stretch of Interstate 495 in Virginia as the state expands its extensive system of high­-occupancy toll lanes closer to Maryland.

The $600 million project will widen the Beltway from the terminus of the 495 Express Lanes near the Dulles Toll Road interchange to the George Washington Memorial Parkway interchange near the American Legion Bridge, which Maryland and Virginia have agreed to rebuild.

When complete, four general-purpose lanes and two new express lanes will run in each direction of the Beltway along that stretch. The road-widening project will deliver the last leg of a tolling system on Northern Virginia’s portion of the Beltway and eventually link to Maryland’s proposed toll lanes on the Beltway and Interstate 270.

Construction will take about three years, officials with the Virginia Department of Transportation said, noting that by the time the new lanes open in 2025, construction on the Maryland side should be in progress.

“Our goal is to have a seamless regional dynamic toll lane network,” said Susan Shaw, director of megaprojects at VDOT.

Virginia transportation officials said the state has finalized contract negotiations with Australian toll operator Transurban, which was selected two years ago to build and manage the lanes. The company on Wednesday said it has selected Lane Construction Corp. to design and build the new lanes. The construction company also worked on express lanes along Interstates 395 and 95.

Early construction, including soil boring and surveying activities, are underway, with full construction expected to start by the end of the year or early 2022, the company said.

The project includes connections from the Express Lanes to the George Washington Memorial Parkway and the Dulles Toll Road, as well as the replacement or rehabilitation of seven bridges. Virginia is negotiating with about 90 property owners in the path of the project, although state officials say no relocations are expected.

“Growing up near Tysons and as a current resident, I have witnessed for far too long the congestion challenges drivers face in this corridor,” Pierce Coffee, president of Transurban North America, said in a statement, adding that the project “is an important step toward providing travelers relief from this gridlock with new travel choices.”

As part of the deal, Transurban will provide $2.2 million annually for transit improvements in the corridor, including new bus service connecting Fairfax and Montgomery counties via the American Legion Bridge.

Virginia transportation officials said toll revenue will help pay for bicycle and pedestrian connections in the corridor. Transurban has also committed nearly $1.4 million for a Fairfax County project to restore part of Scott’s Run, which is intended to improve stream conditions.

Earlier this year, the state pledged $5.2 million for the purchase of new buses to launch a Tysons-Montgomery County route. The plan to launch new bus service across the American Legion Bridge is critical to reducing car volumes in the corridor during and after construction, state officials said. Shaw said Wednesday the state’s goal is to begin transit operations before the new lanes open.

A transit study concluded that new bus service would move more than 170,000 riders each year. The toll lane project calls for four miles of bicycle and pedestrian connections, including a trail parallel to the Beltway connecting to other trails leading to Tysons. The trail will be built to connect to planned paths in Maryland, including pedestrian and bike access across the Potomac River.

A traffic analysis by VDOT indicates that after the project is finished, northbound express-lane users would save 24 minutes in travel time — from Route 123 to the Clara Barton Parkway — during the afternoon rush in 2025, before Maryland’s American Legion Bridge widening and express-lane project is complete.

Virginia officials say the bridge replacement and Maryland’s toll lane project are critical to maximize benefits to commuters. Some critics say without improvements in Maryland, drivers would face a worse bottleneck where toll lanes merge into regular traffic at the bridge.

In a recent public meeting about the project, Maryland transportation officials reiterated the state’s commitment to replacing the American Legion Bridge and to building toll lanes that would connect to Virginia’s network. Virginia officials say they expect Maryland’s project could be finished by 2027, with an overlap of both projects under construction for about two years. Terry Owens, a spokesman for the Maryland Department of Transportation project, said that timeline matches the state’s projections.

The Maryland project has drawn criticism from opponents who say creating the lanes would not be worth harming streams and public parkland or increasing vehicle emissions.

The widening of the Beltway is touted as critical to addressing traffic congestion in one of the Washington region’s busiest corridors. An average of 240,000 motorists cross the American Legion Bridge daily, according to Virginia transportation officials, and northbound traffic backups routinely extend from Tysons to the bridge — even outside rush hours.

By expanding its network of toll lanes, Virginia officials say they want to increase the capacity of the transportation network and give drivers more options. Solo drivers, for example, will be able to use the HOT lanes if they are willing to pay for a more guaranteed trip free of traffic, officials said. Drivers who carpool with at least two other passengers will be able to travel free in the HOT lanes.

The Beltway project is moving to construction following completion of environmental studies that began in 2018 and after the state received clearance from the Federal Highway Administration. Fairfax County also voted in support of the project.

Northern Virginia has more than 60 miles of toll lanes and is building an additional 35 miles. Under construction is a 10-mile extension of the 95 Express Lanes to Fredericksburg and 22½ miles on Interstate 66 outside the Beltway.