A new national traffic-safety study based on an experiment along a two-mile stretch of Leesburg Pike in the Tysons Corner area concludes that car accidents in urban areas can be reduced dramatically by making relatively simple, inexpensive fixes to the roadway.

The study by the Insurance Institute for Highway Safety said that changes as simple as adding a green-arrow left-turn signal to an intersection, extending a merge lane and moving a bus stop by a few hundred feet can reduce accidents at dangerous intersections.

Working with Virginia Department of Transportation engineers, the safety organization chose six intersections in the Tysons Corner area where police reports indicated a pattern in the types of crashes, such as rear-end collisions or left-turning vehicles hit by oncoming traffic.

VDOT made fixes to the intersections, which were monitored from two to 41/2years. The number of certain types of crashes dropped at all six sites, some markedly, though traffic increased during the period.

At Leesburg Pike (Route 7) and the entrance to the Tysons Corner Shopping Center, for example, several crashes had involved left-turning vehicles being hit by oncoming vehicles. VDOT converted the left lane to a "protected lane," in which drivers could turn left only on a green arrow when oncoming traffic was stopped.

After the change, the number of such collisions fell from 8.7 crashes a year to zero over a two-year period.

"To see reductions in the magnitude that we see in this study is very gratifying," said Richard A. Retting, a senior transportation engineer at the institute who directed the study.

VDOT officials in Richmond said they would use the study to make similar changes at other intersections.

The Washington area ranked No. 11 nationally in the number of fatal car crashes, according to the study by the Arlington-based institute, which is a nonprofit research and communications organization funded by auto insurers.

The study said that although most fatal auto crashes happen on the nation's rural roads, about 8,000 deaths and more than 1 million injuries occur annually on streets in and near the nation's cities. In 2003, the most recent year for which data were available, 490 people in the area were killed in urban crashes. Countless hours were lost in traffic jams that resulted from accident scene cleanups and investigations.

In the study, Retting said he was looking for "patterns of preventable crashes. Roads like Leesburg Pike represent a great opportunity to identify easy ways to systematically solve intersection safety problems."

He said this was the first time that researchers set out to determine whether specific types of crashes -- ones that could be prevented easily -- turned up frequently in the crash statistics at certain intersections.

At Leesburg Pike and Lewinsville Road -- another site where left-turn, oncoming crashes were common -- engineers converted the lanes so drivers were permitted to turn left only on a green arrow when oncoming traffic was stopped.

The number of left-turn crashes decreased from 4.6 a year to zero in the 21/2 years after the change.

Although less marked, the changes at the other four intersections still reduced the number of crashes. Painting markings on the road to alert drivers that the right lane was a combined through- and turn-lane led to fewer rear-end crashes where Leesburg Pike intersects with George Marshall Drive and Magarity Road.

At Magarity Road and Leesburg Pike, rear-end crashes were occurring when cars halted suddenly to avoid slamming into buses that stopped in the travel lane for passengers. Engineers moved the bus stop down the street, to where the bus had additional room to pull over, thus reducing rear-end collisions.

At Westpark Drive, extending the distance of the lane where vehicles merge onto Leesburg Pike reduced the number of rear-end crashes, from 8.2 a year on average to less than one.

"In some cases, short-term, less-costly solutions can provide immediate relief with minimal or moderate effort," Retting said. "A lot of these projects can be implemented in-house with state or county employees."

Constance S. Sorrell, VDOT's chief of system operations, said the study is "going to be tremendously helpful."

She said the state agency has plans to adopt the study's model to help reduce crashes at other problem spots.

"We are definitely going to be using this," she said.

Along Westpark Drive, extending the distance of the merge lane toward Leesburg Pike reduced the number of rear-end crashes from an average of 8.2 a year to less than one.After left-turn lanes were tweaked at Leesburg Pike and Lewinsville Road, the number of left-turn crashes decreased from 4.6 a year to zero over a 21/2-year period.