Installation of a traffic control system to test the proposed narrowing of South Arlington Ridge Road has been completed, and test conditions will remain in effect through Nov. 15 between 23rd Street South and South Glebe Road, according to H.S. Hulme Jr., director of the Department of Public Works.

The Arlington County Board made a decision July 9 to conduct the test as part of a study to determine if that section of Arlington Ridge Road should be narrowed from four lanes to two lanes as requested by neighborhood residents.

The board's unanimous action came after dozens of Arlington Ridge residents, who have lobbied for the change for almost 10 years, complained about safety risks from speeding cars when commuters use the road as a shortcut between I-395 and Crystal City and Alexandria.

The street will be narrowed to simulate two lanes by the installation of reflective delineators about four feet inside the curb line on each side. Signs approaches will inform motorists. Lane markings will be blackened, but the solid yellow center line will be retained.

At the approaches to the traffic signals at South Glebe Road and 23rd Street South, two approach lanes in each direction will remain available.

Hulme said that after the test period is completed, the road will revert to the four-lane section until a decision about the proposed project is reached.

A summary report on the test will be presented to the County Board Dec. 10. At that meeting, amendments to the county's Master Thoroughfare and Arlington Ridge Neighborhood Conservation plans also will be considered.

"During the test period, we'll be collecting information on traffic speeds, volumes, accidents and acceptable traffic-flow gaps for drivers using driveways on that section of roadway," Hulme said.

The public may send comments on the test system to Public Works Planning, Court House, Arlington, Va. 22201 or call 558-2941.