Northbound Express Lanes near the I-66. The pavement marks separates the service shoulder on left. (Tracy A. Woodward/The Washington Post)

One of the nation’s best-known highways is getting a makeover for the 21st century.

Early Saturday, a new set of lanes is set to open on the Virginia side of the Capital Beltway, and it’s not just new asphalt. The 495 Express Lanes represent a new approach to paying for highways and managing traffic.

If they work as designed, such high-occupancy toll lanes may be the way of the future for planners trying to cope with the public’s desire for congestion relief and determination not to pay more taxes for a solution.

But this new frontier is lined with questions, not least of which is the role of the private sector in operating a vital piece of the region’s transportation infrastructure.

The partnership of the Transurban and Fluor companies that built the lanes absorbed much of the nearly $2 billion in costs in exchange for the right to collect tolls on Virginia’s newest highway for most of this century.

There is no cap on how high those tolls can rise. The operators will adjust the toll to the demand for lane use, guaranteeing travelers a trip that is quick, consistent and relatively free of congestion. The toll structure also will create an incentive for commuters to share rides, either by carpool, vanpool or bus.

With high-occupancy toll lanes, commonly known as HOT lanes, the government gets a break on the construction costs while giving commuters more choices for getting through some of the nation’s worst traffic.

“The HOT approach provides an option, not a substitute,” said Alan Pisarski, a Northern Virginian who wrote the influential study “Commuting in America.” “Everyone can continue as before, but there is now an opportunity to pay extra for premium service when it is critical to the user.”

But is this new segment of I-495 really the highway of the future?

Don’t look for a quick answer. Although this concept has been applied around the world, the Beltway’s HOT lanes didn’t come out of a box. They include unusual features specific to this market. Peter Samuel, editor of TOLLROADS­news, a Frederick-based Web site that monitors the evolution of transportation policy, said the tolling system is “a very ambitious and complicated format with so many entries and exits.” The project even had to develop a new type of E-ZPass.

At the outset, the quarter-million daily drivers who know the Beltway won’t know the HOT lanes. They may be slow to adapt to the electronic tolling and to the new access points along the 14 miles between Springfield and Tysons Corner. They must deal with left entrances and exits and new red lights at some interchanges.

Since adding four lanes to the Beltway will almost certainly ease traffic congestion overall in the early going, drivers may stick with the free ride in the regular lanes.

The HOT lanes also could have some unintended consequences, changing traffic patterns on adjacent commuter routes.

North of the Potomac River, Montgomery County officials are concerned that the additional lanes on the Virginia side of the Beltway, unmatched by Maryland, will put even more stress on traffic at the American Legion Bridge.

The reason Virginia got itself into this — and the reason other transportation planners are anxious to see the result — is that traditional ways of financing big projects like Interstate 66 can’t keep up with the demand for congestion relief.

Virginia’s government got so desperate to appease commuters that administrations of both political parties agreed on the HOT lanes approach.

At Tuesday’s pre-opening ceremony in Tysons — a bipartisan lovefest with a ribbon cutting and balloon drop presided over by Virginia Gov. Robert F. McDonnell (R)Federal Highway Administrator Victor Mendez noted that “government resources are very limited in today’s world.” The express lanes project, he said, “is a model for what can happen throughout the nation.”

Virginia Transportation Secretary Sean T. Connaughton described it as “a high-tech wonder.” Then added, “hopefully, this weekend it will work.”

He was teasing. Virginia is confident enough in the project’s success to have signed a deal with the same private partners to replace the I-95 High Occupancy Vehicle lanes with HOT lanes and extend them farther south in 2014.

Still, many things new things have to go right.

Few highways in the D.C. area are tolled, and none is tolled like the 495 Express Lanes.

Maryland’s Intercounty Connector, the region’s first new highway of the 21st century, also uses electronic tolling, but the style is known as variable tolling. The rates, highest at rush hour and lowest off-peak, are set.

The 495 Express Lanes will use dynamic tolling. At any time of day, the toll will be based on supply and demand. Sensors along the lanes will feed traffic information to an operations center near the Springfield interchange.

A computer will calculate whether there’s too much demand for the supply of lanes. To maintain the guaranteed speed of 45 mph, it will raise the price of using the lanes. Approaching drivers will see the new rates on overhead messages boards, and some will decide it’s too pricey. They will stick with the regular lanes, easing congestion in the express lanes.

To claim the free ride for a carpool in the express lanes, a driver must not only have at least three people aboard, but also obtain a new type of transponder called an E-ZPass Flex.

The Flex has a switch the driver can toggle between the regular toll-paying setting and another that tells the toll-reading equipment it’s a carpool. State police looking for cheaters also can read that signal.

Nowhere in the D.C. region will the benefits of sharing rides be so obvious. A carpooler need only look up at the message board displaying the toll rates. The average driver probably will pay $3 to $6 for a rush-hour ride, Transurban estimated.

At those prices, the lane operators don’t expect the same drivers to use them every day. But they do expect that when time equals money, drivers will make a calculation in their favor.

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