Bend’s is probably a traffic circle at Reed Market and Bond St. It constantly has tourist traffic for the Old Mill District.
Not to mention it's somewhat of a bottleneck in Bend's street network, even if the Old Mill wasn't there. Reed Market Rd is the farthest south Deschutes River crossing in Bend, so any traffic from south of there that needs to cross the river is likely going to use that bridge (or still be forced through it, eg. using the Columbia St bridge which I often did). I lived in SW Bend off of Brookswood, and I went to middle and high school on the other side of the river, so I was almost forced through that roundabout on a daily basis.
That said, I always thought the light at Reed Market and 3rd St was worse than that roundabout. I would sometimes go way out of my way to avoid that, like going south to Knott Rd to bypass most of the city to get to the NE side. There's lots of bad spots in Bend, really. The signals on 97 in the north part of Bend are some more low hanging fruit.
Even though I live in Boise which is a much bigger city than Bend, traffic is generally not nearly as bad on a daily basis as when I lived in Bend. The worst Boise traffic is worse than the worst Bend traffic (most of the worse "Boise traffic" is in Meridian), but on average Bend is probably worse. Every time I go back and visit Bend, that confirms my feelings on that.