Maryland highway officials, spurred by projections of a staggering increase in traffic on Rte. 29 through Montgomery County, are seriously considering a solution long familiar to highway commuters in Northern Virginia: car pool lanes.

At a public hearing next spring, the State Highway Administration will present a plan to construct reversible car pool lanes down the median of Rte. 29 from Rte. 198, just south of the Patuxent River, to Silver Spring, about eight miles, officials said. They would be the first such lanes in the state.

"No decisions have been made, but more and more support is being generated for HOV {high occupancy vehicle} lanes" on Rte. 29, said Neil Pedersen, chief of planning for the highway administration. Added Mike Snyder, the district highway engineer: "It looks very promising."

Virginia highway planners have long advocated car pool lanes as a means of relieving traffic congestion without building new roads. On Shirley Highway, rules limiting the two reversible lanes down the median to vehicles with four or more passengers have been in effect for more than a decade. HOV rules apply to I-66 inside the Capital Beltway during rush hours. Alexandria has set aside car pool lanes on Washington Street and plans to impose the same restrictions on Rte. 1.

Although buses serving the Shady Grove Metro station are allowed to use the shoulder of I-270, Maryland has been reluctant to follow Virginia's lead in implementing HOV lanes.

"The basic issue is that for an HOV to be successful, you've got to have a lot of people going to common destinations," Pedersen said.

Thus, car pool lanes make sense on Shirley Highway, which funnels traffic directly into downtown Washington, seat of the federal government and the region's largest employment center. But they would make less sense on I-270 in Montgomery County, because that interstate ends at the Beltway, Pedersen said.

"If you have both houses and jobs spread out, it's a lot harder to form car pools," he said.

Rte. 29, also known as Columbia Pike, is beginning to look like a good candidate for HOV lanes, officials said.

Tracing the eastern edge of Montgomery County, it links the ever-multiplying subdivisions of Howard County with the office towers of Silver Spring.

Highway planners expect 58 percent more traffic on Rte. 29 by 2015 -- enough to create bumper-to-bumper traffic from the Beltway to the Patuxent River every morning and evening, six hours a day.

Not everyone has rushed to endorse the idea. In the view of some civic groups, the car pool lanes, and the expanded overall capacity of the road, will simply bring more traffic into Silver Spring, already the subject of intense debate. County officials are considering development proposals there and the implications of such development, including increased traffic.

"We already have too many people in the southern county," said Robert Cordella of the Woodside Park Civic Association. "We know it's just going to bring more cars into the Silver Spring area."

John Clark, the county's director of transportation planning, however, thinks that such views are unrealistic.

"A lot of the growth is in Howard County," he said. "The demand is there."

The car pool lane proposal is being considered as part of a $75 million package that includes widening Rte. 29 to six lanes throughout its length in Montgomery County and building as many as seven major interchanges.

Two HOV lanes, for buses, car pools and van pools, would run as far south as New Hampshire Avenue, where the right-of-way narrows, according to one option under discussion.

After New Hampshire Avenue, one lane would carry HOV traffic into Silver Spring.

Montgomery County officials first suggested that car pool lanes be included in the project in the early 1980s, when it started to become clear that expanded capacity alone would not meet projected demand.

"We realized that development in the 29 corridor was such that it required more than just reliance on the single-passenger automobile," Clark said.

"We need to reward the people who choose to get three people in a car and take up less space, and the reward that the government can give is time savings."

The state will decide whether to build the car pool lanes after listening to public reaction to the proposal at the hearing next spring.

If it decides to go ahead with the plan, a major education campaign aimed at changing driving habits will certainly follow.

"The most successful {HOV projects} have been where there was a time savings of 10 minutes or more," Pedersen said. "Because there's a certain amount of time involved in forming a car pool, a two- or three-minute savings is not going to work."

As an added incentive, county officials hope that car pool lanes on Rte. 29 can be built with underpasses and overpasses so that HOV traffic does not have to stop at intersections.

It's all part of the strategy of persuasion, said Robert McGarry, the county's director of transportation.

"If you choose to drive {alone}, you'll stop a lot," he said.