I don't think it's even a game theory problem, because most of the actors aren't even rationally looking at their options.

In the Pacific Northwest, maybe 20% of drivers are trying to make any decision that will help them. Maybe another 20% are trying to do the best for themselves as long as it doesn't harm the global traffic state. The last 60% are checked out and are barely paying enough attention to not crash.

Using PNW drivers as an example is, well, a bad example. They're collectively so bad that getting onto the freeway in my rental car in any other city in the U. S. is like a breath of fresh air. "Hey, honey, look at that guy: he just moved out of the left lane!" "Wow, it's like everybody in $CITY knows how to merge into a freeway. I want to live here!"

I won't, however, argue with your numbers. Tagging 60% in the "able to aim their car toward Bel-Square without hitting anything on the way" seems about right. And as you point out, it's the cause of much of the traffic woes of the Seattle area, not lack of road capacity. If everyone learned to merge smoothly, and realized it's not their $DEITY-given right to just randomly pick a lane to drive in, we could last another ten years before needing to add lanes.