The presence of the vehicles themselves is an act of intimidation. This could be a reason why Ottawa police have been so timid. Not hard at all to drive forward and injure and kill someone. There's video footage from the Vancouver protest that shows a truck attempting this, and the counter protestor attempting to block the truck had to step aside.

This novel use of trucks for protest has been enormously effective and I expect we'll see this replicated all over from now on.

Whereas in the past it took a mass movement of thousand upon thousands to block a bridge, now a few dozen people in trucks can do the same thing.

Trucks enable a protest to be incredibly paralyzing with a fraction of the amount of protestors.