Traffic moves west on the Dulles Toll Road just past the Wiehle Avenue overpass in June 2010, where the Silver Line of the Metro was being extended to Dulles Airport. (Robert Thomson/The Post)

Metro’s new Silver Line is almost two years from opening, but residents are wrestling with the lasting impact the project may have on local roads.

Users of the Dulles Toll Road are worried because they face higher rates to help pay for more than 50 percent of the rail extension’s cost. Nearby residents express concern that the higher toll rates could push drivers onto already-clogged secondary roadways.

Meanwhile, some businesses wonder whether Fairfax and Loudoun counties might balk at making their full contributions for the 23-mile rail line.

The first phase of the $6 billion Silver Line is under construction from Falls Church to Reston and is expected to open in late 2013 or 2014. Construction on the second part of the project, which will run to Dulles International Airport and into Loudoun, is expected to start in January and be completed in five years.

Dulles Toll Road rates are expected to rise sharply over the next few years. Tolls for a one-way trip that now costs $2.25 could increase to $4.50 as early as next year, according to a consultant’s report for the Metropolitan Washington Airport Authority, which operates the toll road and is supervising construction of the Silver Line. By 2018, tolls for that one-way trip could rise to $6.75.

The increased rates could drive down the number of trips from roughly 100 million a year to 75 million during that period, according to the report. Some residents say those drivers could end up on Route 7, Route 66, Route 50 and other secondary roads, such as Beulah Road and Georgetown Pike.

Already jammed

Terry Maynard, a Reston Citizens Association board member, said, “The big arterial roads are jammed at rush hour right now, and things are only likely to get worse.”

Officials at the Virginia Department of Transportation, however, aren’t as worried.

Hari Sripathi, the agency’s regional operations director, said drivers won’t abandon the toll road — even with higher rates — immediately.

“People are not going to flood the secondary roads overnight,” he said.

Transportation planners said they will make changes to signals or turn lanes if secondary roads are becoming clogged. There are plans to enlarge part of Route 7 from Reston Parkway to Tysons Corner from four lanes to six, he said, which could help handle some additional traffic.

“Not everybody is going to use the arterial streets,” he said. “Some are going to leave their cars and use rail. Some are going to change their travel time or use carpools so that will spread the traffic.”

Others say worries about future traffic may be premature. They point out there is no guarantee that Fairfax and Loudoun counties will agree to pay their allotted share of the costs of the Silver Line’s second part.

The two counties have until early June to decide whether they will support a deal to construct the second phase, at an estimated cost of nearly $3 billion. Loudoun officials have expressed concern about the project’s cost, and the two counties have to determine how to pay for parking garages and the Route 28 rail station.

Businesses are anxiously watching to see what the counties do.

According to a survey done by the Greater Reston Chamber of Commerce, area businesses “overwhelmingly support” the Silver Line project and expect it to be a boon for economic development. The survey included more than 400 individuals in the information technology, nonprofit, real estate and government contracting industries.

Forty-seven percent of those surveyed want to see the second part of the Silver Line extend all the way to Ashburn, its planned terminus. But there has been some discussion of stopping the project at Dulles International Airport.

Bill Byers, executive vice president at First Virginia Community Bank, said his bank opened an office two years ago near the Wiehle Avenue station in Reston and plans to rent additional space — in large part because of the coming Silver Line.

A need for options

Not building the full second phase, he said, would be a “disaster” for the area as the center of population moves west.

“You have got to give commuters options,” said Byers, a Loudoun resident who said he spends $250 a month in tolls on the Dulles Toll Road. “If they have rail, at least they can take it and that gets people off the roads. They’re going to pick whatever option is most productive for them, regardless of the cost.”

Byers said his clients are expanding their businesses in Fairfax and Loudoun because their employees “can’t afford a house in Arlington, so they move farther out.

“But then they have a two-hour commute every day and get home at dark,” he said. “Metro is really going to allow companies to move outside” the inner Beltway.