Maybe a missing traffic sign ?
It's this whole stretch (60+ km) 'till about the gas station/parking, after which they return to normal speed.
![Image](https://abload.de/img/ets2_20230105_223536_dki6r.png)
There are 50 kph signs at the start of the road, but those are for the sharp turns there.
But no sign which says you can drive at normal speed again.
btw, not all AI traffic goes 50, some go fast, maybe depend where they spawn ?
(p.s : tester profile, with only ProMods enabled, nothing else)