It just gets rubbed off and blows away/gets pushed off by cars as they pass over it.
Many end up as the surface of kid's playgrounds these days - shredded and then mixed together into a granule matting..
Some are used as new supports for coral polyps to attach to on reefs - loads of them joined together and placed on the seabed...after a while they are covered in life.
We have to pay upwards of $1 per tyre to get rid of them from our workshop.
Bayview,
In Canada we pay $3 per tire we purchase, for "environmental"..also TV, ipods, computers etc have a surcharge too, depending on their size...and paint cans...pop & liquor bottles/cans..never ending
I didn't mean the visible parts of the tire on the side of the road, I meant when the tires wear away thru normal wear. It must be rubbing onto the road?
Socks:
At one of our apt buildings we have free laundry. When we show applicants this room, we always mention we have a cupboard of unmatched socks..help yourself.