Quebec: How to distinguish autoroutes from other highways?

The legislation in Quebec defines default speed limits (=when no sign overrides this) of 100 km/h for autoroutes and 90 km/h on other paved highways:


Thus, there is a necessity to be able to distinguish roads designated as autoroutes from other national highways. Whether a highway is an autoroute or not, cannot be linked to physical properties of the road (e.g. dual carriageway / all roads tagged as highway=motorway), at least not by law, because


In other words, the law does not dictate any hard requirements for a highway to be designated as an autoroute. How it looks in the reality I do not know, but not sure if it is relevant unless the situation is absolutely unambiguous.

I also noticed that unlike how autoroutes are referred to in the wikipedia, autoroutes in OSM are not tagged like ref=A-20 etc. but simply ref=20.

So, my question: Is it possible to determine whether a highway is an autoroute based on the tags of that highway? Are all autoroutes consistently tagged in a way so that they can be clearly distinguished from other highway?
And, well, if not, what’s your suggestion for a tag that denotes this?


This link will help you clarify. It comes straight from the Government’s geographical data, including those from the Ministry of Transportation: