Vienna-area commuters who drive the I-66 corridor can now carpool into D.C. toll-free and win prizes for doing it.

The I-66 Slugging Challenge, a 66-day carpooling initiative, launched Monday, Sept. 14 and runs through Nov. 20. The program is organized by the I-66 Slugging Network, a coalition of residential groups and public agencies supported through the U.S. Department of Transportation's Small Business Innovation Research program.

Commuters meet at one of two park-and-ride locations, form groups of three or more, and ride together on the I-66 Express Lanes without paying tolls. The driver needs an E-ZPass Flex switched to HOV mode. Parking is free.

The two pickup spots are the Monument Drive commuter parking garage in Fair Oaks and the University Boulevard Park and Ride in Gainesville. Morning lines run from 6 a.m. to 8:30 a.m., with four drop-off points: Rosslyn, L'Enfant Plaza, Navy Yard and Metro Center. Afternoon return lines operate from 3 to 5 p.m.

For Vienna residents, the closest pickup location is the Monument Drive garage in Fair Oaks, roughly a 15-minute drive west on I-66.

No money changes hands between drivers and riders. The slugi66.com website estimates a typical slugger saves about $20 in tolls and 20 minutes per trip.

Participants who register at slugi66.com and log trips through the CommuterCash app earn entries into weekly $100 gift card drawings. The maximum prize total is $1,000 over the challenge's 66 days. Commuters can use the slug lines without registering but won't qualify for prizes.

David LeBlanc, a spokesperson for the I-66 Slugging Network, said in a statement that slugging "has been an effective and efficient commuting solution in the Washington region for decades." He called the challenge an effort to bring the practice to the I-66 corridor, "where commuters urgently need more flexible and cost-effective travel options."

Slug lines have operated along the I-95 and I-395 corridors near Springfield for years. The I-66 network consulted those organizers but is not directly affiliated with them, InsideNova reported.

Separately, Fairfax Connector's Route 798 Express between Tysons and Bethesda is fare-free through Friday, Sept. 18, as part of Try Transit Week. The route is piloting a closed-container policy during the free week, allowing riders to bring a morning beverage on the bus.

The I-66 Slugging Network's long-term goal is to make corridor slugging a permanent commuting option beyond the 66-day challenge.