I encountered this (but avoided due to some route planning beforehand) when travelling to the Le Mans 24 hour race from Dieppe ferry-port, because most if not all routes from the oft-used French port entries from the UK for those heading to Le Mans (eg. Calais, Dunkirk and Dieppe), will take you though Rouen and this City is included in the Crit-air scheme. The easiest route (certainly for Le Mans) is to cross the Seine at Pont bu Brotonne, the first opportunity to do so West of Rouen. There appears to be no route through Rouen without the need of a Crit-air "pass" and we didnt want to take the risk of getting caught without it because it was previously only available as a hard copy via postal services and that was too late (so were we in realising we needed one!). Im pleased to see that it is now available as a "digital copy within 72 hours" but clearly you still need to plan ahead.