Hopefully this will be improved in the new engine. But for now I will follow your advice and just focus on main roads.
Is it better for a crossing to split long path into pieces or a "long" segment is better? What I don't undertstand is how AI cars decide where they should wait. I know how it works for traffic lights.
Also, since you have to adjust the priority for every segment seperately and it's annoying to select the segments if they're small, it's probably easier to generally try to make as few as possible. Not sure if there's any technical benefit to it though.
This is another good advice
It's better to use the long paths and split them only if necessary.
Not really. Sadly one cannot control where the cars stop. They always drive up to the point where they have to give way (where the other path crosses the car's own path). That often leads to multiple cars blocking each other, as the yielding car stops not in front of but on the intersection.
That can be seen in the second screenshot, where the white Golf stops in the middle of the intersection (where the paths are not split) to give way to the car on the right, which seems to be turning left and therefore has to give way to the car on the left, which is already blocked by the Golf.
Most of the time I prohibit all but one or two (opposite) left turns per crossing, as sooner or later there will be some clogging Lotus cannot solve otherwise.
I see, so really there is nothing we can do about this. Hopefully, the AI behavior will be improved in the new engine (streets module and traffic system are planned for 0.3.0).