The Question should be "Why do people congregate at Calais & Duisberg and travel the C-D Road"?
It's because that's where everyone is. It's possibly the only area on the map that you are guaranteed to meet people in the Servers.
In ProMods its the Kirkenes Quarry road. Why? because that's where everyone is.
Are there too many people there? Yes
Should there be a restriction on where you can drive because of number of people? No.
If you sterilise those areas with Non collision zones, eventually there will be a new C-D Road, because those areas will no longer be 'fun' for those that choose to go there.
I'm sorry to say, but in my opinion the only way to 'fix' the area is to have improved game moderation in the areas where the most people are.
The area has been the same for Years. if Moderators don't want to take a shift moderating the areas of heavy traffic, then maybe they shouldn't be a moderator.
If that means TMP recruiting staff specifically for areas like C-D Road & Kirkenes then that's what they should do.
By knowing those areas are under constant supervision, might mean that people are more patient, they might not make as many dangerous overtakes, and may even make some of them slow down a little, because a Kick or Ban will be a certainty not a 'roll of the dice' as it is currently.
Maybe another solution to the problem could be to finally fix the in game reporting system? I guess caravans were a higher priority to have.
TMP can't /fix their way out of this problem.