Theres always the odd post that drags me out of board retirement, and that title did it !!! 

I would gently wrap the poor wee thing and take it to the nearest vet.  The thing with cats (and some other animals) is that they can look very dead and appear not to be breathing as its so shallow. Left on the side of the road some later try and drag themselves home and die en route. 

Swift vetinary action at the post impact stage gives them the best chance, a bit of fluid and meds can make the difference.  If nothing else the vet can pts to stop further suffering and scan for the chip to notify the owner.  There is nothing worse than not knowing what happened and where theyve gone. 😢