The terrible signage around Turin hides this bit of the terrible numbering around Turin, and so this bit of motorway is nowhere referred to as (yet another spur of) A55 on the road.
I cannot remember exactly what led me to make this a part of the A6 (which was more effort for me than keeping it a spur of the A55). I know it was a long, hard decision (partially due to the borderline nature of the decision, partially as I put a lot of thought into it, partially as I spend ages trying to come up with a way to make no change while keeping to CHM rules about routes' signage). A quick look shows me that on top of the A55 number not appearing, A6 km posts seem to count from the northern end of the A55 spur, and the signs heading south actually refer to the A6 (OK, they also refer to the T2, along with myriad other roads, and it is heading to the A6).
Google's number had no effect on it - IIRC, they are copying me (certainly there's other times Google's copied things off CHM/TM where I've been different), and I don't trust their mapping anywhere near enough to override OSM without evidence from other sources (signs, etc).
