There are lots of weird ambiguous traffic situations. The entire Queen Anne Ave going up the hill is unclear. Is it one lane? Is it two? I frequently see people take it as two lanes, but then sometimes jackasses will drive right down the middle of it. It seems to change between one and two just based on peer pressure - if some people are driving down the middle then everyone does, if people are driving it two laned then it's two.
Lanes disappear randomly and without warning. On the aforementioned Queene Anne halfway up the hill it definitely becomes one lane, with no merge warning of course. 1st Ave N where it hits Mercer suddenly goes from 3 lanes to 2 with no warning.
All over Cap Hill here they have a brilliant system where major roads are either 1 or 2 lanes depending on the time of day. They're mostly painted to look like 2 lanes, so you can be driving along in the right lane and suddenly someone is parked in your lane and you have to do a sudden merge or get stuck. It's especially mad because it's on the busiest roads, like Madison, Olive, etc. If you get off the 5 North onto Olive you're immediately in a clusterfuck of lanes mysteriously disappearing and people parked in the right lane (sometimes).
Of course we haven't even got into the lack of pedestrian safety traffic devices.