About 6:15 most mornings, Robert Lang can be found standing in line with complete strangers at a parking lot in Dumfries, waving a sign that says "Roslyn." He tells people he lost the other "s" in Rosslyn on a rainy day.

Whether waiting in rainy, hot or cold weather, Lang helps form a carpool so he can ride on the faster-moving high-occupancy vehicle lanes.

No, the practice is not ideal. But it is effective and, in its way, a reliable commute.

Now, though, Lang and legions of his fellow "slugs," or "sluggers," think their commuting way of life is under assault by state plans to allow drivers to pay for the privilege of joining carpoolers in the high-occupancy lanes on Interstate 95/395.

"I really hate to see someone messing with a system that works," Lang said. "Drivers who are paying a toll have no incentive to pick up passengers. Eventually, the slugs will go away."

It's unclear how slugging started, but lore dates it to the early 1970s, when commuters hoping to form carpools for the HOV lanes would gather at bus stops. Slug is the term for a fake coin in a bus farebox, and it is believed bus drivers characterized the waiting carpoolers that way because the commuters, though at bus stops, were not riders.

Carpoolers come to sprawling exurban parking lots in the wee hours with the "don't-do-this-kids" hope that a stranger will pull up to offer them a ride to work. The practice requires a high degree of trust, not to mention an admirable degree of tolerance for their fellow humans, but slugs said it beats the exorbitant amounts of money, time and mental strain that come with driving alone in the crowded regular lanes.

Over the years, they have formed their own language and rules. Lines form in set spots. Drivers must not "stop short" -- end a ride before the established destination. Passengers do not speak unless spoken to.

Their peculiar practice -- the only other known successful slug system is in the San Francisco Bay Area -- is a significant boon to traffic. Virginia officials said that most of the 35,000 or so carpoolers who use the I-95 HOV lanes daily are sluggers. If the system broke down, they said, those people probably would drive themselves, adding thousands of cars to the highway.

As Virginia pursues plans to build high-occupancy toll lanes on many of its major highways, slugs have emerged as an outspoken force against them. They fear for the future of carpool lanes, which they said will be overrun by toll-paying customers.

"Within five or 10 years, they're going to eliminate HOV completely," said Scott Hirons, a slugger from Stafford County who started the Committee to Save HOV to fight the I-95 proposals.

HOT lanes generally are free to carpoolers, and others can use them for a fee. The lanes are characterized as a congestion-free way to commute because tolls are raised as traffic escalates to prevent clogging.

Virginia officials have embraced the concept and turned to the private sector to finance them in return for some of their toll revenue.

This year, state officials, working with Fluor Inc. and Transurban Group, announced plans to build HOT lanes on a 14-mile stretch of the Capital Beltway. And this month, two private proposals were submitted to build HOT lanes in the I-95 corridor. The proposals allow carpools of three or more to continue using the lanes free.

HOT lanes have been popular elsewhere, and there was scant opposition when Virginia officials unveiled the Beltway plan. But I-95 is different.

"We have a very successful and highly utilized HOV lane that could be harmed," Bob Hugman, a Woodbridge slug, said in an e-mail. "The slugging community is defending what we consider the 'crown jewel' of HOV commuting."

The two plans, each of which would cost about $900 million, envision adding a third lane to existing HOV lanes in the northern parts of the highway; extending those lanes south to the Fredericksburg area; adding commuter parking lots; and augmenting bus service.

Slugs are skeptical that they will continue to be allowed to ride free. They point to California, where carpoolers in Orange County said they were given the same promise but now pay half-price during some peak hours.

Area carpoolers said they also fear that many drivers will decide to pay a toll rather than pick up passengers.

"Right now, people are cutting back on carpooling because the HOV lanes are getting crowded," said slug Corey A. Stewart (R-Occoquan), who is a member of the Prince William Board of County Supervisors. "With the addition of toll-paying autos, you lose the incentive altogether to carpool."

Virginia transportation officials said such worries are unfounded. "This is a big change, so there will be people who are concerned and have fears about preserving HOV and slugging," state Secretary of Transportation Pierce R. Homer said. But, "Those used to carpooling today, their world will change very little and, in fact, improve because of additional resources on enforcement."

Gary Groat, director of project development for Fluor, said there are no plans to charge carpoolers or restrict their access. He also said there would be more incentive to pick up sluggers because that would save drivers from tolls.

But Groat acknowledged that plans could change if the lanes fill with free riders. "It's a function of what traffic is like 10 years from now," he said.

Slugs said a better solution to ease congestion would be to build more commuter lots; enforce lanes better; end exemptions; and raise HOV requirements to four people per car.

"Why can't we be presented with some other options?" Hugman wrote. "Instead, the HOT lane process goes on like a steamroller."

Assembled carpool passengers, or "slugs," line up in the morning at a commuter parking lot in Dumfries as they wait for rides.