Protesters who jammed morning rush-hour traffic on Interstate 93 for miles yesterday by chaining their hands through 1,200-pound concrete-filled barrels — even resulting in two ambulances being delayed — won’t rule out a future stunt.

“There’s nothing currently planned,” said James Billman, 25, of Brookline, who was one of 29 protesters arrested and arraigned yesterday. “But I can’t say whether there’s a possibility of it happening again.”

Another protester, who declined to give his name, said, “I don’t know,” and smirked when asked if he planned to return.

The protesters said they staged the blockade to call attention to racial injustice in the wake of police killings of unarmed black men in New York and Missouri.

Billman and 10 other protesters were arraigned on numerous obstruction and disorderly conduct charges at Quincy District Court for blocking off I-93 North in Milton. Eighteen others were arraigned at Somerville District Court for similar antics on I-93 South in Medford.

The protests trapped thousands of drivers in a crawling commute and caused potentially dangerous delays for ambulances, including one carrying an 83-year-old accident victim, when they rolled out the concrete-filled barrels from a truck onto the road and chained their arms inside holes left in the drums.

“There were two autonomous groups. Our group was on 93, but the group in Somerville was a different autonomous group,” Billman told the Herald. “I don’t think I know anyone who was associated with that.”

In Quincy, friends of the supporters sat quietly in the courtroom and refused to comment later.

Police said some of the I-93 protesters in Milton were wearing diapers under their clothing — an indication they intended to block the highway for hours.

“Their plan, obviously, was to stay on the highway for a long time,” Massachusetts state police spokesman David Procopio said.

The protests started at about 7:30 a.m. and were broken up under an hour later, but traffic was not flowing until after about 10 a.m.

Boston Mayor Martin J. Walsh blasted the Expressway protests.

“I think by upsetting and confusing and scaring a lot of people is not the way to get your message across,” Walsh said. “From what I understand, a lot of the protesters did not live in the city of Boston, did not live in the state of Massachusetts. My message to you if you are coming to this state to disrupt things, don’t.”

State police Col. Supt. Timothy Alben called on lawmakers to block such highway sit-ins, and state Rep. Timothy Whelan (D-Barnstable) yesterday filed legislation that would create enhanced penalties for those who would block travel.

“Think about everything that is going on in the world today, not just here in Boston or in our country. Think about terrorism events,” Alben said. “Now we have an unmarked van that is going to stop on an interstate highway and unload three large barrels with an unknown material — what are you thinking as a citizen out there using the interstate? What’s going through your mind when you see this kind of action and activity?”

Erica Moura, Richard Weir, Marie Szaniszlo and Prisca Pointdujour contributed to this report.