Maybe because it is a workshop map that uses the two lane highway instead of the normal freeways in either direction? That's really the only thing that's different. I watch this happen and it is ALL 'tourists' in their motorhomes and RVs. I had to make that little roundabout because they were going all the way into town to turn around on and clog my dead end streets. The traffic enters the city limits (red lines), exits the highway at the first off ramp, finds the first intersection they can, immediately turns around and leaves the city the same way they came (blue lines). I see something strange going on in my city and I don't know how to correct it, if I can.