Virginia Gov. Robert F. McDonnell announced Tuesday that the state has made a formal agreement with private partners to build 29 miles of high-occupancy toll lanes along Interstate 95. Construction is scheduled to begin very soon and should be done by the end of 2014.

The agreement is similar to the one already in place to build the HOT lanes on the Capital Beltway between Springfield and the Dulles Toll Road. Those four new lanes are scheduled to open by the end of this year, and will eventually link up with the HOT lanes on I-95.

The projects will offer a significant change in commuting styles to many thousands of travelers in one of the nation’s most congested regions. But many of those commuters have yet to embrace the change.

Proponents, including both Republican and Democratic gubernatorial administrations over the past decade, say the HOT lanes will offer reliable trips at decent speeds for those willing to pay a toll while providing a free trip for those willing to carpool.

Skeptics, who include many of those potential drivers and carpoolers, deride the HOT lanes as “Lexus Lanes,” a privileged commute afforded to those wealthy enough to afford a variable toll that has no cap.

Still, there was little doubt that the I-95 HOT lanes would reach the stage that the governor announced Tuesday. The Virginia Department of Transportation has been working on this with the private partners building the Beltway HOT lanes. A tentative deal was announced in December. Test borings have been underway for a while, and an August groundbreaking has been anticipated.

According to the governor’s announcement, the agreement with 95 Express Lanes LLC, a joint venture between Transurban DRIVe and Fluor Enterprises Inc., covers construction and operation of 29 miles of express lanes on I-95 from Garrisonville Road in Stafford County to Edsall Road in Fairfax County.

“This is a historical day for transportation and the economy in Virginia,” McDonnell said in a statement announcing the deal.

Part of the route covers the High Occupancy Vehicle lanes between Dumfries and Edsall Road, but the lanes will be extended south to Garrisonville Road.

The northern portion, the 14 miles between the Prince William Parkway and the Edsall Road area near the beginning of I-395, will go from two to three lanes. Cutting off the HOT lanes project at that point was a decision the McDonnell administration made after Arlington County filed a lawsuit challenging the original plan to provide HOT lanes all the way north to the the approaches to the 14th Street Bridge at the Potomac River.

The project will add some park-and-ride lots and expand others for those who want to carpool.

In 2012, the governor’s office said, there will be 600 more spaces at the Saratoga/EPG park and ride lot in Fairfax County and 700 spaces at the Telegraph Road-Old PRTC bus garage park and ride lot in Prince William County.

By end of 2014, there will be 1,000 spaces at Staffordboro Boulevard in Stafford County and 1,000 spaces at Gordon Road in the Fredericksburg area. A new 1,000-space garage will be built along with the new Potomac Nationals Stadium at Stonebridge in Prince William County.

The HOT lanes, which will be known as the I-95 Express Lanes, will operate the same way as the new Beltway lanes. They will be toll free for vehicles with three or more people aboard, and for motorcycles. Those who don’t meet the HOV requirements will pay a variable toll.

Everyone but the motorcyclists will need an E-ZPass transponder to use the lanes. The carpoolers will need a new style of transponder called an E-ZPass Flex, which just became available in anticipation of the 495 Express Lanes opening.

Planners anticipate that drivers will pay the toll only when circumstances require that they make the trip faster, or at least can be sure how long it will take. While the toll will rise with the level of traffic congestion, the governor’s office announcement anticipated that a typical trip during rush hour would cost $5 or $6.

Construction will cost $925 million, the governor’s office said. The private partners will put up $854 million. VDOT’s share will be $71 million.

Proponents say that such public-private partnerships are one of the few ways to build big new highway projects, since there is little chance of increasing gas taxes or finding some other way to raise money through public financing.

Opponents, including the Coalition for Smarter Growth, said Virginia did not adequately consider alternatives to this approach.

VDOT will own and oversee the new lanes, an arrangement comparable to the Beltway deal. The consortium known as 95 Express will finance, build, operate and maintain the new lanes as part of a 76-year concession.

The private partners assume the risk of delivering the project on a performance-based, fixed-price, fixed-date contract, the governor’s office said.