Virginia's Transportation Department plans to install video detectors to ease traffic congestion along Route 7, one of Northern Virginia's most heavily traveled commuter routes.

The video detectors, an advance over the highway sensors in use today, are among the small, relatively inexpensive techniques that transportation agencies throughout the region are employing as money for large construction projects becomes scarce.

Beginning in January, detectors perched high above traffic lights at up to 20 intersections between Tysons Corner and Leesburg should make commute times a little shorter and more consistent for the up to 72,000 drivers who use the highway each day, the Virginia Department of Transportation said yesterday.

The devices, which resemble large flashlights in cylindrical protective tubes, shoot digital images that represent traffic volume and speed and immediately convert them into a code recognized by VDOT's traffic control system.

No one can watch traffic with these detectors, unlike the rotating, zooming cameras that link to Fairfax-based Web site, which allows commuters to see real-time images of selected highways.

VDOT's monitoring system, which collects traffic data from more than 12,000 lightly electrified metal loops in the pavement, is vulnerable to damage. Snowplows and utility crews are regular threats.

The devices "become dumb," said Tom Farley, VDOT's district administrator. Red lights could pop up even when no cars are at an intersection, he said.

Grindingly long commutes are familiar to Route 7's drivers.

"It's a horrible, scary ride when it's stop-and-go and the lights are not green for long enough," said Donald Bland, 52, a bus driver and nighttime security guard who lives in Herndon.

"I think I've changed my life so I don't have to go down [Route] 7," said Laura Poindexter, 34, a personal trainer who regularly traveled from Arlington to Sterling starting 11 years ago to visit her then-boyfriend.

She married him. They now live in Sterling, and both still get caught in traffic.

The video detectors cost less than $1,000 each and are less vulnerable to damage than highway sensors. But the accompanying technological and computing changes raise the price to more than $10,000 per device. U.S. Rep. Frank R. Wolf (R-Va.), whose district includes the Route 7 corridor, said he secured $500,000 in federal funds for the video detectors.

The number of intersections actually covered will not be determined until a contractor is selected later this summer. Installation will begin in November and last two months.

Commuters are eager for traffic improvements, but not all are optimistic about the new detectors, which VDOT says should improve traffic flow slightly.

"Unfortunately, I just don't believe you can help the problem of congestion without widening the space," said Robert Phelan, 29, of Sterling, who owns a home improvement business. "Volume is volume. It still needs a place to go."

But even small improvements in traffic signals can be a good thing, others said.

"Catching all red lights is just as bad as heavy traffic," said Eric Clements, 20, of Charles Town, W.Va., who works at Giant Food in Sterling.

At VDOT's Smart Traffic Center in Arlington, employees use monitoring systems and video cameras to follow the flow of vehicles throughout Northern Virginia.