(Disclaimer: I am a traffic engineer in the sense that I have a degree in it and have done it professionally, but I got disillusioned and bailed in favor of software engineering so I’m not hugely experienced. Think EIT, not PE.)

That is a very good question I don’t have a good answer for, and have wondered myself.

First of all, it’s more in the wheelhouse of urban planning than it is traffic engineering (being concerned with an entire area rather than one road at a time), so there’s that. But on the other hand, urban planners are more concerned with issues like land use and aren’t necessarily analyzing traffic flows the way traffic engineers do. I’m not sure the specific kind of comprehensive designing you’re hoping for actually gets done often enough.

That said, it seems like the prevailing opinion (when it comes to the city street network, as opposed to freeways) is that having a hierarchy of functional classification, with the traffic being funneled from local streets to collectors to arterials, is the preferred way to go. Traffic engineers like it because they can (theoretically) design the arterial to provide better performance in terms of mobility while worrying less about pesky things like access and placemaking, and NIMBY homeowners like it because it gets the thru-traffic off their street.

Personally, I’m actually pretty skeptical of that, from an urbanist and “recovering engineer” perspective. I think it could be better if traffic were evenly distributed across blocks, such that (a) the lack of true high-capacity/high-speed corridors would discourage driving altogether and provide better placemaking and urbanism, and (b) each street’s “fair share” would hopefully be low and slow enough that it would be acceptably safe for cyclists/pedestrians/kids playing in the street etc. Basically, I think “worse” could actually be better, once you realign your goals away from moving traffic as quickly as possible and towards making a good place to live.

When it comes to freeways specifically, I’m not sure anywhere does parallel freeway corridors unless the area served by each justifies a freeway in its own right. But if anywhere does, it’d be Texas, home of the infamous Katy Freeway…

Katy Freeway

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…and other extensive use of frontage roads. I actually learned about that just the other day from this recent Road Guy Rob video, which honestly might answer your question better than my screed above did, now that I think about it. (Sorry for not leading with that, but I’ve got too much sunk cost fallacy to delete what I wrote now.)