> How can a car be dangerously slow if all the other cars stick to the speed limit as well?

Because the other cars are speeding too.

> Notably, any reduction in danger that flows from breaking the speed limit is only for the car and other cars breaking the speed limit, in no case it is for pedestrians, cyclists or other non-vehicle participants in traffic.

Correct.

Speed limits in a vacuum are largely about revenue generation. There's ample evidence backing numerous practices that actually slow traffic, things like using traffic circles instead of intersections, reducing the width of lanes to promote slower travel, speed humps, separating traffic that's going a distance (roads) at speed, from slower traffic preparing to enter residences/businesses (streets). Lots of stuff.

Limits though? I mean they probably don't do nothing but they aren't nearly as effective unless you pair them with a regular police presence. And even then, mixed effects. I'm pretty sure the entirety of the Chicago Loop is capped at 55 mph, but if you actually do 55 on that thing, you're gonna die.

As to the topic of the thread: truthfully, IMO, parents should be barred from ferrying their kids to school. Not only is it just a "commute but worse" in terms of ecological impact (the car goes, drops the person, returns home, then returns later, picks up, and returns home. Literally 2x the normal traffic impact) but also it's ridiculously inefficient for similar reasons. School traffic everywhere I have ever lived has been a goddamned nightmare. I would rather be stuck on the highway jam ten times than be trying to navigate around a school full of stressed, harried parents driving big stupid SUVs, who themselves are surrounded by children, who themselves are entering and exiting vehicles at random.

School busses are the safest vehicles on American roads, and starting kids on them early gets them comfortable with the idea of mass transit. Dictionary definition of a win/win.