It's chopped up old tyres that they use for the pellets on astroturf pitches is it not?
I think the UK standard ones don't have as much nasty stuff in them as exists elsewhere (the US for example) although that's them being chopped up and not burnt. I don't think I'd want to be anywhere in the vicinity if they were being burnt.
It would be surprising if the motor industry didn't have a protocol in place for the safe and environmentally friendly disposal of the millions of used tyres we inevitably get through every year.
All garages have to pay for the removal of old tyres and it's not cheap. My old boss looked into a tyre shredding machine as a possible earner but the cheapest machine came in at about a quarter of a million so he's still thinking about it.