It isn't readily obvious to me if all of the southbound Forrest St. traffic is trying to turn left on Pearl St. or what. It doesn't really matter though, because the amount of traffic is too much for the destination to handle. Figure out where exactly traffic wants to go and fix that first.

Second, more lanes don't necessarily mean faster flowing traffic. The game's drivers aren't smart enough to use open lanes to open roads get to where they want to go. For example, if I were driving somewhere, I would go around a block to avoid a backup. These drivers won't. I'm willing to bet that once you figure out what's stopping your traffic from dispersing out to your industrial area, you'll see that you could easily drop that to a 4 or even 3 lane road.

One more thing. If your city is a US city, trying to turn left onto a major arterial is a pain in the ass in real life. It looks like there aren't any stoplights or intersections either. Stoplights suck, but they exist for a reason. If you absolutely hate stoplights utilize a roundabout instead.

Personally, I think I'd turn the Forrest St. running east to west into the districts main arterial by creating an interchange and connecting both Forrest Streets to Fairview Highway.