The so-called "People's Convoy," which originated in California and has drawn participants from around the country, is calling for an end to all pandemic-related restrictions. It was inspired by demonstrations last month that paralysed Ottawa, Canada's capital city.
Leaders of the convoy on Sunday said that on Monday they will again slowly drive the Beltway, a 105-kilometre highway that encircles the city, though details of when the action would take place were not known.
Hundreds of vehicles gathered on Friday and Saturday at the Hagerstown Speedway, a racetrack in Maryland about 120 km northwest of downtown Washington.
On Sunday morning, many left in convoy to drive two slow laps on the Beltway. They honked their horns as they set off, while onlookers waved American flags, according to a Reuters witness.
The convoy, more than 2 miles long, slowed traffic at points along the Beltway by late Sunday morning, but did not bring it to a standstill. It returned to the Hagerstown Speedway in the afternoon, according to messages on the convoy's Telegram channel.
The convoy's protest against vaccine requirements and other pandemic restrictions has been undercut in recent weeks as major US cities have rolled back mask mandates and other measures against COVID-19 with infections and hospitalisations declining dramatically.
President Joe Biden, a Democrat, signalled in his State of the Union speech on Tuesday that the country was entering a new, phase of the pandemic without business lockdowns, school closures or other daily disruptions.
At the racetrack on Friday night, one participant who described himself as the lead trucker told a cheering crowd he would drive his truck into the heart of the American capital.
"DC, the government, whomever, can claim that they have all this opposition for us waiting in DC," the man said. "But that flag on the back of my truck will go down to Constitution Avenue between the White House and the Washington Monument."
US federal law enforcement agencies have been coordinating with state and local authorities for weeks in preparation for the possible arrival of the convoy, according to one US official who requested anonymity to discuss internal operations.
