I've lived in Tucson for over two years, and comparatively speaking, traffic is not bad here. There are a few projects that need to be finished, for example there's a gap in the widening of Houghton Rd. along the east side of the city that would fix things in that area a lot. The city maintained portion of SR 210 Aviation Hwy desperately needs repair. Irvington Rd. east of Davis-Monthan AFB needs widening as well. The city and Pima County have both made some interesting design choices in some intersections that you don't really see elsewhere (Valencia and Kolb come to mind), but overall traffic moves well for a city this size.
I've noticed two things that contribute to "bad traffic": protected left turns are at the end of a signal cycle within the city limits, with flashing yellow arrows preceding them. There are many intersections where it's double left turn lanes in each direction and the sight lines for a confident turn with the flashing yellow are not always there. As an almost civil engineer that didn't finish his degree, I'm surprised at some of the choices for flashing yellow double-left turn lanes. And secondly, speed limits in parts of the city that are basically open desert or 3 or 4 lane in each direction arterials are set artificially low. The new stretch of the Houghton Rd arterial south of I-10 is a prime example: the speed limit is posted at 45 MPH. Once you come to the end of the arterial and join the older two lane roadway, the speed limit increases. There are many places where the speed limits seem low or even arbitrary, and this creates the effect of drivers ignoring all speed limits.
I would also advocate for finishing the arterial routes that have not been widened, where it's wide on either side of a particular stretch. Needless bottlenecks are, well, needless bottlenecks. The unusual intersections, such as Valencia and Kolb, or Grand and Euclid, definitely deserve some commendation for innovation. Although I have to wonder if the extra amount of ROW required makes it worth it more than just once in a blue moon.
In terms of the signal operations, this is actually where Tucson is known for their creativity. They were one of the first to widely implement double left turns, and remain one of just a handful of cities that implemented permissive phasing even with double left turns. There have been quite a few studies early-on that showed a very small increase in accidents, if any at most intersections, but an impressive increase in capacity. I believe this policy (implemented sometime during the 1980s) is when the city started practicing lagging left turns as well. The city also experimented with a
small gore area between the through lanes and double left turn lanes; this changes the left turn design from negative offset to either no offset or positive offset, improving visibility for left turning traffic dramatically. Both of these innovations are what made Tucson's intersections more successful than typical intersections in other cities IMO.
I know Tucson, in the last ten years, has started to change how their signals operate, with time-of-day phasing and flashing yellow arrows rather than 5-section "yield on green" type signals. Switching to
lagging left turns EDIT: flashing yellow arrows technically eliminated one of the more annoying aspects of lagging green arrows
with shared signal faces, which is that both directions have green arrows simultaneous with one another, regardless if it's necessary. We have this issue in Japan (complete with permissive double turns) where our green arrows are always at the end, and it's not always great for roads with uneven traffic flows. Thing is, I don't know if Tucson actually changed their signals to allow for "offset" green arrow phasing (where the green arrows come on at different times). If they haven't, I could see that being a smart change. I would also like to see wider implementation of left turn waiting boxes, other than just a couple spots along Speedway at the UA Campus.
Edit: massive brain-fart in the last paragraph. WTF...
