The Virginia state government has decided to enlist a private partner to build and operate the high-occupancy toll lanes on I-66 outside the Capital Beltway.

That’s the same concessionaire style of project development that the state used to set up the HOT lanes on the Capital Beltway and on I-95/395. But for I-66 outside the Beltway, the state also considered using a more traditional building and operating approach in which the state would take primary responsibility.

The announcement during Tuesday’s Commonwealth Transportation Board does not tell us who the private partner would be. That decision is likely to be made during 2016, based on bids the state will receive. VDOT expects that the maximum public contribution the project would be $600 million. The private concessionaire would bear the financial risk if the traffic volume in the HOT lanes and the resulting toll revenue fails to meet its expectations.

The state would be required to compensate the private concessionaire if either of these two things happened: If the state added regular lanes to I-66 within the outside the Beltway corridor; if the Orange Line were extended west within the first decade of the concession.

There would be no provision in the contract for compensating the concessionaire if free carpooling in the lanes went beyond a certain percentage of the total traffic.

The decision about using the public-private partnership approach does not affect the design of the project. Under the plan, I-66 would be rebuilt to have two HOT lanes and three regular lanes on the outside the Beltway portion by 2021. Also unchanged by this announcement is the plan for the state to develop the I-66 HOT lanes project inside the Beltway, without this partnership approach.

Virginia Transportation Secretary Aubrey Layne said he saw no problem synching the two portions of the project. The state plans to convert the High Occupancy Vehicle lanes inside the Beltway to HOT lanes in 2017.

Layne also said that the state should retain the option of going for a publicly financed project outside the Beltway until a contract is signed, to ensure that the potential private partners maintain the favorable progams they have laid out for the state in their preliminary discussions.

Those discussions, which have not been in public, had led Virginia officials to conclude that they can save money by enlisting a private partner and still get the support system they want for carpooling, commuter buses and other forms of transportation that allow people to leave their cars behind before traveling on I-66.

“We always said we were going to follow the numbers,” Layne said. However, he said, the commonwealth is prepared to do the project on its own if a snag develops in private negotiations.