There should be a legally allowed speed at which one may drive through highway-blocking mobs, and it should be at least in the low double digits
You protest on the sidewalk. You attempt to imprison folks on the highway, and that imprisonment is a potential precursor to assault for which folks should be allowed to defend themselves and/or effect their escape.
It's like Pope John Paul II used to say, "Don't walk on the freeway unless you wanna' get hit by a car"