| They're torn up from the road and rubbed off from the tyres themselves. The majority is obviously coming from the road. There's been studies done here in Sweden since we've banned studded winter tyres in some areas of Stockholm in an effort to reduce road wear and improve air quality. I don't know of any sources in English off the top of my head though. The last time I read an article about it though (2+ years ago, during Diesel-gate), the findings was that the danger in the particles comes from their size with smaller particles being more dangerous for humans. And that road particles were something like an order of magnitude larger than exhaust fume particles from diesel engines. We've since banned diesel engines inside Stockholm as well so the whole thing is moot here. |
Not sure even that adds up to believable.
The Sydney Harbour Bridge is about 500m long between the pylons. It has "more than 150,000 cars per day" on it (according to the snippet from a google search). If all of that was from the road, that'd mean there's about 160 tons of road getting torn up per year. It looks to be ~30m wide on Google Sat view, and "google first hit" research indicates road base weighs 1.9tons per cubic meter. It's be losing almost 6cm of depth along the whole span every year if all those numbers hold, or 3cm per year if "only half" of that comes from the road and the rest from the tires. They don't resurface it anything like often enough for that to be true...