>The bitumen-modified plastic improved the tensile strength of the road by making it more durable and flexible. Plastic also prevented pothole formation. When the layer of molten plastic filled the space between the gravel and bitumen it thwarted rain water from seeping in and causing structural defects.
Seems like it would break down less than a regular tar-only road and last longer to boot.
It seems like it will help keep the overall rigity of the road but it says nothing about how the material will break into pieces on the exterior layers. Plastics are known to cause cancer and other harm to living things when ingested, and my curiosity is if plastic could be more damaging than the thing it replaces.
Myself, I'm not convinced plastic is more harmful to the immediate environment in this application than the tar/bitumen itself. It does seem the issue of plastic shedding into the environment has not been investigated enough, but does tar not leech toxic chemicals as well?
Seems like it would break down less than a regular tar-only road and last longer to boot.