Morning commuters traveling east on the Dulles Toll Road will pay a 25-cent toll to exit at Rte. 7, the Virginia Highways and Transportation Department announced last week.

Currently, morning rush-hour backups of between one-half and one mile are common at the exit, which highway officials believe motorists use to avoid the toll plazas just to the east, said highway department spokeswoman Lynda South.

"The point is that Tysons traffic can use Spring Hill Road to avoid the backup, and they're not doing that," said South. "The reason for the toll is so we can distribute traffic more evenly. We're hoping people will find it's not worth their time to drive through Tysons Corner and will go through the main toll plaza."

The highway department has not set a date for the opening of the Rte. 7 toll booths, but it will be "no sooner than this summer," said South.

Although Fairfax County does not have jurisdiction over the state road, Supervisor Martha V. Pennino (D-Centreville), attacked the plan at Monday's Fairfax County Board meeting.

"The backup at the main toll booth during the rush crunch in the morning is horrendous," said Pennino, who is the board's vice chairwoman. If another booth goes in, "it will back up to Reston, where we already have a backup at the toll booths."

The toll at the main plaza, designed for traffic heading for the Beltway, is 50 cents; the toll at Spring Hill Road, on either side of the main plaza booths, is 25 cents. The two new tolls at the Rte. 7 exit, both for eastbound traffic, will only operate between 6 and 10 a.m., weekdays. The main toll plaza and the Spring Hill Road exit operate 24 hours daily, although Spring Hill is staffed only from 5:30 a.m. to 6:30 p.m., Monday through Saturday. Exact change is required at other times.

To serve motorists who had been exiting at Rte. 7 and who choose the main toll plaza or Spring Hill Road as a result of the new toll, the highway commission will install two new booths at the main toll plaza, one in each direction, plus an additional booth in each direction at the Spring Hill Road exit.

The Federal Aviation Administration, which owns the land on which the toll road was built, has given the state permission to operate the new toll booths for a one-year trial period.

Pennino is skeptical of the tolls as a way to clear Tysons Corner congestion, because, she said, highway officials came up with the plan on the basis of a faulty assumption.

"They say that in the morning rush hours, commuters come off the toll road at Rte. 7 and proceed eastward, rather than stay on the toll road and pay the tolls," said Pennino. "I opposed that concept because people in my district, in Reston and the northwest part of the county, use the toll road to get to work in Vienna and the City of Fairfax, Westgate, Westpark and Tysons. They ought to do a survey of destination. If they've done a survey, they certainly haven't shared it with me."

While the highway department has not done a destination survey among motorists exiting at Rte. 7, a January traffic count of eastbound vehicles performed during a peak morning hour found that 2,920 cars exited at the main toll plaza, 1,535 exited at Rte. 7, and only 367 exited at Spring Hill Road, the exit "originally designed to serve Tysons Corner traffic," said South. "You can draw your own conclusions from that," she said.

"I'm concerned about the proposal," said Board of Supervisors Chairman John F. Herrity. "I may not support it -- I don't have enough facts and I don't feel like asking people to pay another quarter.

"There are a number of projects that will be finished in months. The extension of International Drive which eventually will connect Spring Hill Road with Rte. 123 and Gallows Road , the overpass over Rte. 7 at Gallows Road, widening 123 -- all these are projects that are funded, under way and should significantly help.

"Traffic at Tysons is not the best situation, but there are worse situations," Herrity said.