I think “traffic stop” is a poor choice of words. It’s not like they were stopped for a broken taillight, speeding, etc.
They were arrested on a federal felony charge of conspiracy to impede U.S. officers from discharging their official duties. The stop was to affect the arrest.
“traffic ambush”
But isn't that what every protester does?
Doesn't a bunch of people carrying signs and blocking the sidewalk "impede U.S. officers from discharging their official duties"?