In spite of poorly marked interchanges and the general unfinished condition of the new Dulles toll road, officials of the Virginia Department of Highways and Transportation said this week that the $56 million commuter artery in western Fairfax is already near capacity during morning and evening rush hours.

Highway officials said estimates of rush hour traffic are based on visual inspections because existing equipment cannot give hour-by-hour counts on the number of cars going through the tollbooths. They said more than 40,000 cars a day are using the road, a figure that the department had projected would not be reached until the end of the first year of operation. The toll road opened Oct. 1.

Highway officials said commuters face backups during rush hours at the Rte. 7 and Reston area exits. The toll road parallels the Dulles Airport road from Rte. 123 near Rte. I-66 and Tysons Corner west to Rte. 28 near the Loudoun County line east of the airport.

Highway officials said the high volume of traffic has forced motorists using the road to drive below 55 mph. "In the morning, the rate drops to 25 to 30 miles per hour," according to Thomas Farley, assistant director for planning and administration for the Northern Virginia division of VDH&T.

Traffic on the road has increased 23 percent since its opening, according to Toll Road Manager Philip DuMars. Based on statistics for two recent weekends, traffic using the road on Saturdays and Sundays now equals 77 percent of weekday usage, DuMars said.

While highway officials said 40,000 cars are using the road daily, the number of cars actually paying tolls during January totaled more than 57,000 per day. The 40,000 figure takes into account the fact that some cars pay at two tollbooths, while others exit at Rte. 7 without paying a second toll, VDH&T officials said. Since the road opened, 6.4 million cars have passed through tollbooths at various ramps and the main toll plaza at Spring Hill Road, DuMars said.

After a flurry of activity by state officials to open the road on schedule even though it was not finished, work on the 13-mile highway slowed dramatically. Commuters using the road daily have complained that exit ramps are not completely paved, few permanent tollbooths are in place, lighting is sparse and signs alerting drivers to exit ramps and ramps leading to the airport access road are insufficient.

Highway officials said overhead signs will be going up at the west end of the toll road beginning this week. Officials said the problems with signs started at about the same time the road opened because the department was working with three contractors. "We thought some signs were going to be in place that were not ," Farley said.

Farley said that almost all the existing signs "are less than desirable. They are meeting a temporary need. Nobody thinks they are permanent." Stacks of new signs were piled along the sides of the parallel lanes last weekend.

Farley said recent bad weather has prevented workers from replacing temporary signs with permanent ones that would be up to the standards of signs marking exits on routes I-95 and I-395.

Farley said some of the exit ramps, including those at the Hunter Mill Road exit, are not finished but that some guardrails have been installed because of severe drop-offs.

Steel barriers dividing the parallel lanes from the airport lanes going in the same direction will not be installed. Instead, VDH&T has opted to use cables as barriers because "we don't want a vehicle bouncing off a fixed barrier. We would rather have the car in the median," Farley said.

Commuters also complained about the lack of lighting between the main toll plazas at Spring Hill Road and Hunter Mill Road where the road corridor is illuminated only by the lights from the few houses near the toll lanes. The lack of lighting can surprise drivers accustomed to brightly lit interstates, officials said.

Farley said those who use the toll lanes are going to have to get accustomed to a lack of lighting. "The only lights are at the toll plazas and the ramps. For the long stretches where there are no lights, most people are used to it," Farley said. He suggested that those planning to use the toll lanes for the first time allow extra time to get to their destinations.

Farley said the road was built as a commuter artery and will be used primarily by those who use it regularly and know where they are going.

One of the major trouble spots for motorists is at the intersections of the toll lanes and the Capital Beltway, where signs seem to appear just about the time motorists should be switching to the far right lane to make the exit when traveling east from the Loudoun and western Fairfax areas.

The average number of daily commuters tossing 50 cents into the main tollbooths increases monthly along with increased usage of ramps between the main tollbooths and Rte. 28, indicating an increase in use of the road by local residents.

Predictions of reductions in traffic loads on Rte. 7 as a result of the opening of the toll road have apparently come true. James Lewis, chairman of TYTRAN, a coalition of Tysons Corner area business and political leaders seeking solutions to transportation problems, said Monday that his group has hired a consultant to do a study comparing current traffic congestion along Rte. 7 with traffic problems prior to the opening of the toll lanes.

DuMars predicted a heavy increase in use during off-peak hours. "We saw that during the holidays with traffic using the toll lanes to enter the Tysons Corner area.