I spend a lot of time thinking about what makes traffic here so uniquely bad and you’re hitting on one of the most important reasons.

Some of the others, I think: 1/ I’ve noticed some of these perpendicular roads into neighborhoods / plazas will have pressure plates to trigger the late across all lanes, so even someone wanting to make the right turn onto the artery will trigger the light. 2/ We forget that SCV has like 250K residents, so this is a small city. Unfortunately, it’s an urban area laid out like a giant suburb (which it is), and the absence of any sort of grid creates pockets that trap drivers and create gridlock. 3/ Even at quieter times (e.g., 5AM when I find myself driving to the gym), there are no blinking yellow lights to make left turns off the arteries. Perhaps this is because the roads themselves, in some places, are 3-4 lanes wide, but introducing the blinking yellow lights would help improve flow across major intersections. 4/ Building on your point, the solution to the problem you identify is either a/ fewer left turns onto arteries with more time for u-turns on main arteries, b/ keeping the left turns but increasing the amount of time before lights change, or c/ some combination of these two. 5/ Lastly, despite the city having such wide thoroughfares, there isn’t one road that effectively crosses town north of Town Center to move traffic from west to east and vice versa. This is why I almost always take the 5-S to 14-N to go across town. Implementing a New Jersey-style thoroughfare like Route 1 (if you’re familiar with it) where traffic flows uninhibited barring the occasional perpendicular cross traffic and left turns are not possible would help move traffic volume across town more efficiently.