How good are American roads?

I heard a civil engineer make a claim once that the dust on the side of the road is about 300% more laden with precious metals like platinum, than random mining. I suppose this is all roads and not just American roads, though.

Isn’t it supposed to be mostly brake pads, rotors, and tire rubber?

Would be fascinating to imagine it being economically viable to vacuum up and reprocess it, but based on the above I’ve assumed it was worthless.

Dust from the catalytic converter. I've heard of gangs in LA taking shopvacs to the shoulder of the freeway at night.