Rush hour traffic along Interstate 66. (Photo by Nikki Kahn/The Washington Post)

Virginia has secured a $1.2 billion federal loan for the construction of toll lanes on Interstate 66 outside the Capital Beltway, Gov. Terry McAuliffe announced Thursday.

The low-interest loan allows the private consortium called I-66 Express Mobility Partners— a group of companies building, operating and maintaining the lanes— to secure the project’s financing package.

The cost for design, construction and right of way is estimated at $2.3 billion. State transportation officials say additional investments in the corridor, including transit improvements, raise the project’s price tag to $3.7 billion.

The expansion of I-66 spans 22.5 miles outside the Beltway. It will add high-occupancy toll (HOT) lanes from University Boulevard in Gainesville to the Beltway. In addition, there will be three general-purpose lanes in each direction, a multiuse trail in portion of the corridor, and new and expanded transit service, including additional park-and-ride lots, and median space reserved for future rail service.

The state recently released final designs for the project, which will be available for public review and comment this fall. The Virginia Department of Transportation has scheduled hearings for Nov. 13, 14 and 16.

Major construction is slated to start next spring, but some early construction activities — such as utility relocation, clearing and grubbing, and erosion and sediment-control — may start by the end of the year. Residents are looking at five years of construction, and the express lanes slated to open in 2022.

As a separate project, the state is readying to open HOT lanes in the 10 miles inside the Beltway this year.

The Transportation Infrastructure Finance and Innovation Act (TIFIA) loan, approved the U.S. Department of Transportation, will cover about 33 percent of the project’s total cost, officials said.

“Securing a TIFIA loan was critical to the Commonwealth and its private partner’s ability to move forward and deliver this important public-private partnership transportation project,” McAuliffe said.

Financial close for the overall project is expected next month.