Phon's post in [ANSWERED] [PC] can calais please be a non collision zone? was marked as the answer
Please check out this question as well for some more insight.
NCZ cities are not a permanent thing. Duisburg being made into a NCZ was just a trial and a coping method while we were working on new modifications to the city, because the previous ones broke with a game update. As Luna explained above, other projects have meant that progress on the Duisburg rework is slower than we had hoped, however it is still an ongoing thing and will happen eventually.
Our Add-On Management and Game Moderation Management are actively looking at Calais to see what we can do to improve the traffic flow, in the form of map edits such as traffic lights or different prefabs for the F7, etc. Making it a NCZ is not something we plan to do, as we feel that the traffic flow in Calais is already far better than in Duisburg so there is no need to make the city a NCZ.
Thank you for your question.