Don't get me wrong: traffic engineers aren't out there designing whatever they want with reckless disregard for [driver] safety. In fact, I would say that they're probably more conservative than other types of engineers in terms of following established practices (especially since civil and especially traffic engineering is often more about customizing known-"good" designs to the circumstances of the site, rather than trying to innovate/improve performance the way a mechanical engineer working on a new airplane design might be).
The trouble is, the established practices themselves are wrong and bad in a lot of ways, in particular that they have a very 1950s view of what the goal of the engineer is (moving cars as fast as possible) and don't take enough consideration of the ways that an urban street is very different than a rural highway.
Chuck Marohn of Stong Towns does a very good job of explaining it. He's got a book and long-form videos, but I like citing his "30 days of confessions" playlist of short videos. In particular, as someone working in aviation, you might be interested in "#8 Plane Crash vs. Car Crash", but I recommend watching them all.

I'm not the person you asked, nor have I been going around defending Platner, but I have to admit that I don't know what to believe. Between so much bullshit and disinformation floating around in general (especially against progressives/socialists), and remembering what happened to Al Franken in particular, it's all too conveniently-timed and politically-motivated for me to trust the accusations.
I'm not going to go to bat for the guy (especially since it's a moot point now anyway, obviously), but I'm not going to join the character-assassination dogpile either.