Yeah, but I doubt he'd do that - at least as a sniper. He obviously prefers to catch them out in the open, where a clean shot is assured, rather than inside a vehicle with windows rolled up. Not saying it couldn't happen, but I doubt it.
On the other hand, all that stalled traffic in one neat line would make a handy target for terrorism of a different sort. Blech.
That's where my mind was wandering to... (Even if this sniper isn't a terrorist, they're learning a lot from this)