Ok, here's pics to clarify my above writing;

(pic 1) Here is one of the junctions of my 6 laners. Since all connecting roads are minimum 3 lanes, you get plenty of dedicated turning lanes dividing traffic up nicely. And, since all nearby junctions are designed the same way, you can also see that traffic will use all turning lanes, as they predivide to go left/straight/right at the next junction.

(pic 2) Heres my 'feeding sytem' for my 2 central 6 laners. The road coming in from the right leads directly to my industrial area, and with downtown consisting of high density commercial it generates a lot of traffic. At the left you can see the short 2 lane sections that feed traffic to the center of the 6 laners, which causes traffic to use more lanes from the start. Non of the crossings you see have trafficlights, which is important for a good in and outflow of the busy downtown.
The 2 laner at the left connecting both 6 laners is there to prevent traffic that want's to turn around coming from the left to use the roundabout, but can take the shortcut instead. It's a 2 laner to prevent traffic lights.
One more thing to notice is the two 2x3 laners connecting to the top and bottom of the roundabout. Since it uses 3 laners, it causes a dedicated turning lane on the roundabout itself, which in turn causes traffic to use both lanes on the roundabout, alleviating pressure on the roundabout. Without those 2x3 laners connecting, all traffic would only use the outer lane of the roundabout.

(pic 3) Here's the feeding sytem on the other end of the central 6 laners. It connects directly to the highway (which is at the bottom of the pic, running left to right out of sight). It was even busier then the other one, and was suffering from minor traffic jams. To alleviate pressure, I made 2 shortcuts through the middle of the roundabout to seperate straight from turning traffic on the roundabout. I used highway onramps for the shortcuts, as they have a higher speedlimit, so they will be preferred by traffic going straight. (or else straight traffic might as well opt for using the rounddabout itself.)
These shortcuts cause no traffic lights, because the feed from/onto one way streets. They don't work if you connect them to a two way, because they will cause traffic lights then. Then I also made seperate offramps for traffic wanting to go left from the highway, so that traffic bypasses the roundabout completely.(seen at the left bottom)
It might seem complex, but I'm only applying a couple of basic rules to regulate traffic with my 6 laners;
- Have trafficlight free in and outflow
- Use 2 laners to feed traffic into the center of your 6 laners
- Have minimum 3 lane junctions to create dedicated turning lanes
It's good fun playing around with traffic! Really loving it
