Regional transportation planners yesterday approved a study of the effects of widening the westbound lanes of Interstate 66 in Arlington County, restarting an effort that had faded in recent years because of intense opposition and a lack of money.

Unlike most proposals concerning widening I-66 inside the Capital Beltway, a study was welcomed by both supporters and opponents because they said the results would bolster their positions. In addition to weighing the need for a wider road, the study would consider a "no build" option, transit alternatives and high-occupancy vehicle (HOV) and high-occupancy toll (HOT) lanes.

"We don't have any preconceived notion of what the outcome might be," said Tom Farley, Northern Virginia administrator for the Virginia Department of Transportation.

The idea of widening I-66 inside the Beltway has been debated for years -- virtually since the road opened in 1982. Proponents say the highway is too small to handle growing rush-hour traffic in both directions. And since the Sept. 11, 2001, attacks, they have argued that it is necessary for emergency evacuations of the nation's capital. Opponents say more cars will just add more traffic and air-quality problems to Arlington as well as encourage the kind of suburban sprawl that necessitates paving over more of the region.

Plans for the road have been dormant since 2001, when a major study of both sides of the highway was dropped by the administration of Gov. Mark R. Warner (D) after officials learned that the state didn't have the money to pay for all its promised transportation projects.

The current study was initiated by Reps. Thomas M. Davis III (R-Va.) and Frank R. Wolf (R-Va.), longtime supporters of widening the road, who secured $724,000 in federal money to fund it. Warner agreed to the plan on the condition that it would consider a range of options and include input from the public.

The study, approved yesterday by the Transportation Planning Board, will cover about six miles of the westbound lanes from Scott Street in Rosslyn to the Dulles Access Road just across the Fairfax County line. It will be confined to existing right of way, and officials hope to complete it in eight months.

Backers of a wider highway said a study would conclude what everyone already knows: that more lanes are needed to handle traffic demand in a booming region.

"Frankly, a study isn't necessary to know that more capacity is needed on I-66 inside the Beltway," James Larsen, a spokesman for the Dulles Area Transportation Association and Loudoun County Chamber of Commerce, told board members. "Mounting congestion in this stretch can easily add 10 minutes or more to a trip in either direction."

Larsen's only criticism was that the study didn't include the eastbound lanes of the highway.

Wolf said the study would prove that a third lane is needed and that none of the other options would ease traffic in the area. "You cannot solve the transportation problems of Northern Virginia without widening I-66 inside the Beltway," he said. "It's already a mass transit corridor. I don't think there'd be any downside because it's using the current footprint."

Several opponents of a wider road said they supported the new study because it would show that increased carpooling and transit would solve the corridor's problems.

"We believe that a fair and comprehensive study . . . will conclude that widening is unnecessary, ineffective and unwise," said Jason Rylander, president of the Arlington Coalition for Sensible Transportation.

Arlington resident Allen Muchnick said that a study of the I-66 corridor was "long overdue" and expressed confidence that it would show that increased HOV enforcement and increasing the HOV restriction from two persons per vehicle to three would be sufficient to unclog the highway.

Adding a third lane "would only worsen congestion by impeding HOV enforcement, decreasing motorist safety, delaying the response to incidents, diverting trips from transit and inducing more sprawl," he said.

Tom Farley, VDOT Northern Virginia administrator. Rep. Frank R. Wolf said the study would prove that a third lane is needed on westbound I-66.