Private car routes are generally spread out because they are calculated for different cities at different times, so the alternative may have easily been more congested at the time. This is not really the intended outcome of the congestion mechanic but I don't know if much can be done about it without increasing the check frequency of the routes.
I don't think this is a bug. I think it's a specification.
At least for now, even player convoys don't automatically choose faster roads.
Priority is given to routes that can go straight as long as they are passable. Because the process of searching for a route ends when the route to the first destination is found.
(https://i.imgur.com/ITrBlVD.png)
Ranran automatically selects different routes for going and returning. (Of course none of the roads are one-way)
(https://i.imgur.com/8KedpNh.gif)
This shows that the auto-determined route is neither the shortest nor the fastest.
If the player knows a detour route that can drive faster, he will usually set a waypoint there.
Quote
Expected outcome:
All private cars use the faster way.
QuoteThis is not really the intended outcome of the congestion mechanic but I don't know if much can be done about it without increasing the check frequency of the routes.
I don't know much about private car routing, but does it perform advanced processing that even player convoy does not?
I think that searching for the fastest route even though it is passable will greatly increase the processing. Because there are so many possibilities in the map that you have to check them out. Even so, I think currently private car routing has a lot of performance absorbed.