NBCWashington

Dozens of drivers of tractor-trailers and pickup trucks expressed their frustration over trucking industry regulations and the government shutdown Friday in a way that was guaranteed to get attention: They slowed traffic on Washington's Beltway in a rolling protest.

Those participating in the "Truckers Ride for the Constitution" rally had said they planned to circle the inner loop of the Capital Beltway "three lanes deep" Friday morning.

About 30 commercial vehicles and 15 pickup trucks, many sporting U.S. flags and "#T2SDA" placards, crossed over into Maryland on I-495 northbound at around 8 a.m., Virginia State Police spokeswoman Corrine Geller said.

Nearly an hour later, four tractor-trailers began driving side-by-side, slowing traffic to 15 mph. Virginia State Police say they stopped four tractor-trailers participating in the rally after they slowed traffic.

State troopers stopped the trucks at mile marker 53 and warned them not to impede traffic, Geller says. They were not given a ticket and were allowed to continue.

Around 10:15 a.m., about a dozen truckers returned to Virginia via the westbound lanes of the inner loop, but they were met with already congested traffic caused by heavy volume and weather conditions.

Geller says there have been no major incidents as a result of the convoys.

A Facebook page for the rally had more than 59,000 likes and about 3,000 RSVPs -- a far cry from the number of actual participants seen Friday.

Organizers say the three-day rally was scheduled for a holiday weekend to reduce harm and to allow others to participate in their cause.

A Virginia State Police spokesperson says additional troopers will work through the weekend to respond to any incidents that may arise.

In 2007, a similar rally was held to protest illegal immigration and competition from Mexican truckers,  U.S. News & World Report said. But it did not heavily affect commuters.