Lots of potential there but it will take hell of a lot more than a few pipe bombs
It only takes 10 “protestors” to shut down an entire freeway these days. In a just world, the bastards should have been turned into roadkill where they stood. I suppose if they got hundreds of jihadis to block freeway exits over a couple mile stretch, people would finally flatten them.
More likely, the jihadis would commandeer multiple gasoline tanker trucks and ignite them on multiple exits and on the main freeway.
All one would have to do is stop the lead row of cars, then have teams of killers ready (even in some of the cars at a specific time) mop up from the rear while a small team prevented escape from the head-end.
It would be a murderous slaughter.
And, adequate reason to keep the AR in the trunk.