The Dulles Toll Road, the Washington area's first toll highway in modern times, has been open for nearly a year, and Virginia highway officials say the number of commuters traveling the road has surpassed their initial forecasts.

The four-lane, 13-mile highway, which will mark its first anniversary tomorrow, is used by an estimated 60,000 cars, trucks and buses a day -- 50 percent more than the 40,000 vehicles initially predicted by highway officials. Shortly after the road opened last Oct. 1, traffic totaled only 26,000 vehicles.

"The growth has been phenomenal," said Lynda J. South, a Virginia Department of Highways and Transportation spokeswoman. "The counts and the toll revenues pretty much tell the story. People like the road. They're using it. Time is money."

Toll collections have amounted to $8 million so far, $1.6 million more than expected, South said.

The road, financed by $56.7 million in state-authorized revenue bonds, straddles the Dulles Airport Access Road, extending from the eastern edge of Loudoun County through northern Fairfax County to the Capital Beltway, I-66 and routes leading to downtown Washington.

Because of increased traffic, along with backups at some points, the highway agency is considering several possible improvements, South said. These include constructing an additional lane, converting shoulders to traffic lanes at rush hours, and imposing car-pool restrictions during rush hours or on some lanes.

In addition, South said, commuters can avoid backups at the the exit leading to Rte. 7 by switching to the Spring Hill Road exit. No toll is collected at the Rte. 7 exit. The toll at the Spring Hill Road exit is 25 cents. "They can avoid the backup by paying only a quarter," South said.