A Reston citizens group on Monday said it expects thousands of vehicles will divert from the Dulles Toll Road to local streets as tolls rise in coming years to help pay for Metro’s new Silver Line.

The Reston 2020 Committee, which is part of the Reston Citizens Association, predicts weekday traffic on “corridor area roads,” including Route 7 and the east-west streets in Herndon and Reston, could increase by at least 30,000 vehicles in 2014 — the first full year Phase 1 of the new Silver Line is in operation. Tolls are expected to rise to $4.50 each way by that year.

“The tolls will be doubling in 2014,” said Terry Maynard, a member of the Reston 2020 Committee and the group’s board. “That’s going to drive a large portion of toll-road traffic to local roads, and the local roads are already crowded. The congestion will be that much worse.”

The first phase of the Silver Line is under construction and is expected to open in late 2013. Construction of the second phase is expected to start in January 2013.

The group based its findings in part on a study done by CDM Smith, consultants for the Metropolitan Washington Airports Authority, which is overseeing construction of the rail extension, and information from the Federal Transit Administration. The CDM Smith study predicted declines in transactions on the toll road as rates increase.

The Reston 2020 Committee expects that between 2014 and 2030, daily traffic volumes on local roads could rise by an additional 25,000 to 35,000 vehicles as drivers look for alternatives to the toll road. By then, toll rates are predicted to cost $10.75 each way, according to its report titled “The Dulles Corridor Transportation Planning Fail.”

Tammi Petrine, co-chair of the Reston 2020 committee, called the report evidence of how “awry transportation planning has gone.”

“Anytime a $6 billion public transit system generates more congestion on local roads, we see an abysmal failure,” Petrine said in a statement. “The huge problem is the outrageous tolls.”

Mark Treadaway, an MWAA spokesman, said the CDM Smith study “didn’t look at traffic diversions.”

“We can’t determine the validity of the various assumptions they made in their report,” he said.

Treadaway said MWAA, state and counties officials are looking at various ways to bring down the cost of the project’s second phase.

Revenue collected from the toll road goes in part to help pay for the $6 billion Silver Line, an extension of Metrorail through Tysons Corner to Dulles International Airport and Loudoun County. Seventy-five percent of the nearly $3 billion price tag for the second phase of the Silver Line is expected to be paid for by Dulles Toll Road revenue.

Loudoun and Fairfax counties have until this summer to decide whether they are going to help pay for the second phase.

Some leaders in Loudoun County have expressed concern about the project’s price tag, and politicians in Virginia have threatened to ask the state to withhold money if there is a mandatory project labor agreement on the second part of the project.

The Reston group said it is also worried that few people will ride the Silver Line. They say that many people who would use public transportation are already using Metro’s Orange Line — by either driving to the Vienna station or taking express bus connections from Fairfax or Loudoun counties to West Falls Church.

“When a public transit project drives increased congestion on local roads and requires the huge subsidies envisioned here, something is very wrong with the transportation planning,” the Reston group wrote in its report.