Tire dust is a problem, but i’m not sure it counts as a very big one when compared to the sheer scale of the damage to both people and ecosystems climate change will do. Between ocean acidification and the subsequent collapse of marine life, more frequent and intense hurricanes, floods, wildfires, and droughts, it would take a lot for microplastics to enter the same scale of devistation wrought by over a hundreds of millions of cars dumping more than five metric tons per year of CO2 into the atmosphere.

To reduce microplastics in North America your looking at fighting the car obesity ecidemic, improving tire lifespan, convincing people to be more gentle on the accelerator, fixing the god forsaken mess that is trying to ship anyone less than a thousand tons of aggregate by rail, and of course reducing the number of people who try and use a car to get around a city by expanding rapid rail transit/ increasing telework opportunities.

Outside of maybe some incidental improvement in tire lifespan and chemistry though, I’m afraid I really don’t know how you expect a raceing circuit to be able to help with any of the above.

That would require investment in public transport, and completely redesigning most (US) cities.

Not to mention increasing dependency on rail delivery for cross country goods.