Epic guide indeed. A bit complicated at first but it really works even if you can follow it roughly. Like driscojs mentioned try to avoid intersections and corners. A less complicated thing to do if you just want to get through the campaign mission is a circle and then connect intersections on it.
To make a circle follow the pictures V
First make a cross with roads
The connect all the sides with roads so you can make a circle like this
Now remove the internal roads and in you want to external too in case the intersection is not meant to be a cross
Use it to connect your roads on it.
This is nothing compared to FPs awesome guide but ever since i picked it up in the forums here it has helped a lot with traffic jams in intersections.
Also this is the reason why droscojs said NO corners and as many curved lines as possible.
I just put a corner in a perfect straight line that never had traffic and see what happened :
The car in the middle the has a red circle stopped for some reason making the one that was coming behind it stop too
Here you see on the bottom with the arrow the one that had an arrow above and its stopped. Why its stopped? But because for some reason the one on the picture above decided to stop for a bit even after passing the corner. And yes the other 2 cars are stopped too. .
And just another randomly stopped car here
Why all these cars stop though? Maybe its because the pedestrians pass the crosswalk.. maybe because the chcken tried to cross the road.. maybe they are badly programmed.. who knows the sure is corners are bad and you should avoid as much as possible. >.<!