People in this thread are way too hung up on the "what if cars get attacked" problem. Just because you can't solve every problem, doesn't mean you can't have a usable product.
Cars today don't have any defense against people dropping bricks or pouring paint off an overpass, but somehow the system still works.
I'm not sure humans have the reaction time to avoid an object thrown from an overpass.
On the contrary, over the years I've read on many occasions how drivers and passengers have been seriously injured or killed by the morons who get a kick out of dropping objects from an overpass.
Cars today don't have any defense against people dropping bricks or pouring paint off an overpass, but somehow the system still works.