Millions of miles on the road, I-4 in Orlando . . I-75 in Atlanta. . . Where does all the worn off tread go?

50's tires were rubber and bio-degradable, current tires are complex compounds. If it were bio-degradable . . seems like the tires would self-destruct sooner. Where is all the debris / shreds going ? Seems like you would have piles of it along the interstates.