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.