Lines of honking SUVs, pickup trucks and motorcycles, flying flags for US President Donald Trump are raising security concerns, election experts say - particularly on the country's last day of voting.
One of the caravans, known as "Trump Trains," sparked a confrontation on a highway outside Austin, Texas, on Friday, when it surrounded a campaign bus for Democratic presidential candidate Joe Biden, and one member allegedly sideswiped a car, leading to an FBI investigation. On Sunday, a Trump caravan in Richmond, Virginia left the roadway to drive on the grass near the Lee Monument, Richmond police said on Facebook. Members allegedly pepper sprayed a woman, police said, and they are investigating reports that an unoccupied car was shot.
A slew of Trump Train events are planned for Tuesday, the United States' official Election Day, according to posts on Facebook and interviews with organizers. Several are advertised as ending or going past polling stations. Election security experts say they are concerned the rallies could break laws, intimidate voters or spiral into violent confrontations.
"The Austin thing shows that it's not noise," said Michael Greenberger, the director of the Center for Health and Homeland Security at the University of Maryland.
"Disruption tomorrow is going to be the kind of thing that we haven't seen in our prior federal elections," he predicts.
Most Trump Train events have gone off peacefully, and the three organizers who Reuters spoke to Monday stressed that they condemn what happened in Texas.
A Reuters review of public Facebook events Monday afternoon found about a dozen "Trump Train" caravans planned for Election Day. More are likely to be organized through private groups, experts said.
Several public itineraries include plans to drive past, or through, polling locations. State and federal laws make voter intimidation illegal, and many states have laws against campaigning on or near polling stations.
One such event, organized on Facebook in southeastern Maryland's Wicomico County, outlines a route that goes past the Civic Center and the "election office." The organizer, who gave his name as Mark F. when contacted through Facebook, told Reuters the caravan of vehicles plans to slowly drive through the parking lot of the Civic Center, one of the county's nine voting centres.
Election officials have asked him to change the route, he said, but as of Monday afternoon he hadn't decided whether to accede to their request and drive on the road next to the site instead.
"There's nobody that can stop us," he said, arguing that Trump supporters had the right to be on county property making a last-minute appeal to voters. "I'm going to let everybody know that Biden's not the way to go," he said.
He timed the event for about 3:15 in the afternoon, when he said he thinks the site will be most heavily crowded with voters.
Trump retweeted a video of the Austin caravan on Saturday, commenting "I LOVE TEXAS!" The Trump campaign didn't immediately respond to a request for comment about Tuesday's planned caravans.
Greenberg, who is advising officials on security at polling places, said he hoped the incident in Texas would deter more extreme Trump supporters.
"I think having the FBI saying they're looking at Austin may cause some people, not everyone, to think twice about interference."