LittleDudeWithMuscles saidOne that didn't make the list -- but should have -- is St. Louis. I used to live there. Worst drivers I've ever seen: Scary, angry, dangerous, discourteous, sometimes irrational.
I used to fly into St. Louis quite often, take a rental car to the USAR Personnel Command on (9700?) Page Blvd. for various official reasons. I think it's been relocated since then. In any case I didn't find the traffic terribly bad, and I'd drive around for a few days to restaurants & such, did the Gateway Arch, all that good stuff.
I like Seattle drivers, very efficient & predictable, especially on I-5 and 405. Few lane changes, unlike the Miami area, where they practice the "zig-zag" school of driving.
Traffic flow in Seattle is very smooth & constant, despite a heavy volume on freeways. By not changing lanes every 100 yards like in Miami the traffic flows more quickly, and drivers get into the lane they need to exit early, no last-second swerving across multiple lanes like we experience here, that forces drivers to brake to avoid a collision. That in turn creates a magnifying cascade effect, so that 40 cars back the traffic comes to a standstill, when it could be flowing smoothly.