(1) Whoever was the traffic engineer that designed two major highways merging onto a two lane tunnel was not a very forward thinking individual who'd take into account ever increasing car-traffic. They must be related to the traffic engineers that designed Settler's Ridge.
(2) No matter how bad traffic can get, the sights are simply breath taking. When you're driving into town and you come across that tunnel...you come into the skyline at just the perfect distance. Far enough to see it all, but close enough where you know it's a unique "first-view" of a city.