I think Mt. Carson was never intended for it's current use, much like Kenmount was never meant to be the huge road which is currently is. Mt. Carson during regular hours is actually pretty good, it's during peak traffic hours that everything goes to shit. I remember sitting in traffic trying to get down Carson through Commonwealth on a Friday evening a few years back, it took about 40 minutes to get to my destination once reaching the backlog of cars on Mt. Carson
I really hope that TGH does relieve some of the traffic, but I'm still skeptical about it all.