The organized demonstration on the freeway began Wednesday shortly after 9 a.m. and brought traffic to a standstill on one side of the freeway.
California Highway Patrol officers were at the scene as several violent skirmishes broke out among frustrated drivers and the protesters, who locked arms with each other in a row that spanned across the southbound lanes.
An occasional motorcycle would break through the line and drive onward on the empty freeway ahead.
Protesters calling for cease-fire in Gaza shut down SB 110 Freeway in downtown LA
The activists initially ignored the CHP's orders to disperse. Shortly before 10 a.m., officers began approaching the protesters individually, tying their hands with zip-ties and taking them into custody without incident.
CHP declared an unlawful assembly and all lanes reopened around 11:30 a.m.
The 42 people were all cited for unlawful assembly and have since been released.
Asher Kaplan of IfNotNow LA said the group has been "raising a lot of awareness about this issue. But, unfortunately, the United States government has not made any substantial moves to change what's happening."
IfNotNow LA is made up of American Jews and allies demanding an end to U.S. military aid and support of Israel and asking for a cease-fire.
The group "often engages in divisive rhetoric, some of which may be offensive to members of the mainstream Jewish community," according to the Anti-Defamation League.