Just a quick post regarding advice on a route from Calais to Le Mans avoiding the Rouen CritAir zone. One of the cars in the group won't classify for any zone, and therefore can't go through.
I generally avoid Rouen too - I go via Honfleur (A29) to Caen (A13) and then N158/A88/A28 to Le Mans. 5 Hours ish from the French side, driving smartly on your own - considerably longer in convoy... have done both.