Chris2306's post in Is being too slow bannable? was marked as the answer
I guess it depends on how slow you are on the C-D road and the Game Mod itself, as there's a lot of traffic going on. I've seen a lot of people asking this. So, you shouldn't be too slow for a certain time as it might be considered as blocking, for example something between 10-30 km/h, but Game Modertors usually warn first before doing anything, but you'll get kicked or teleported to the service station if you ignore them.
"§2.3 - Blocking*
Restricting a user's travel path, blocking entrances to highways or other entry points or anything similar. Failure to use the service feature (F7+Enter) when needed might result in a punishment."
You can read the rules there: https://truckersmp.com/rules
Also, you might want to get a more powerful truck when you're driving on the C-D route, so this doesn't happen. For example 750hp and a 6 gear or don't drive a heavy cargo on that route with less powerful trucks.
I hope this could help you!