Traffic in Seattle was bad in 2001.
Part of the problem is bizarre road planning. Unless things have changed, when northbound on I-5, there is only one lane of the five that goes all the way through town without forcing a lane change or an exit. (This doesn't include the lanes reserved for multiple occupancy vehicles.)
In traffic that is heavy to begin with, frequently required lane changes just make things worse.
The 520 floating bridge was a nightmare at rush hour. Made the mistake of riding it on my Harley a few times, and about wore out my clutch hand. I understand there have been some engineering analyses questioning the integrity of the concrete on the floats for the 520 replacement bridge, so that should make things interesting for some time to come.
The other part of the problem, IMO, is limited amount of land available to expand the interstate and major roads.
I used to prefer driving N-S on Hwy 9, and avoiding Seattle entirely, unless my plans involved actually going to Seattle. (Don't get me wrong, Seattle is a great place to visit and do things, but it's often miserable to transit.)
All that said, if I could afford the land I require, and if my wife's family weren't mostly centrally located in NW MO, I'd do my best to convince the wife to move up that way.