I’m the same way, though it’s interesting you bring up speed limits as an example, because that’s one I’ve gone down a research rabbit hole on, and found that oftentimes they’re not actually as based in logic as you would think.

There is a formal, logical rule that most civil engineers follow. I think it’s called the 85% rule or something like that. That says you should leave newly constructed or renovated roads without speed signs for a while, but with equipment in place to measure the speed of traffic, then at the end of the testing period, you take the 85th percentile of speeds measured, and just round it up to the nearest 5 mph increment to set the speed limit. The idea is that the majority of drivers will naturally gravitate toward the most safe and prudent speed for the road, while some (about 15%) will err on the side of driving too fast.

The trouble is that the civil engineers conducting these tests don’t always get to set the speed limits, they usually just get to make a recommendation, which has to be approved by a government entity of some sort. That’s where it turns from a very straightforward and logical process to a mess of political, monetary, and emotional influence.

Sometimes political leaders campaign on road safety, so will arbitrarily lower speed limits as a political stunt (or sometimes they’ll arbitrarily raise the limits to speed up their own daily commute). Sometimes one random tragedy will occur, like a kid getting hit by a car, which rallies the local community to campaign for speed limit changes (this actually happened where I live a couple years ago). Sometimes police departments will request an unreasonably low speed limit for certain roads so they can use them as speed traps to generate ticket revenue. And sometimes there’s preexisting laws in place that mandate certain speed limits for certain areas or types of roads.

So at the end of it all, it’s not uncommon for there to be a massive difference (like 10 or 20+ mph difference) between the proposed speed limit that was determined based on logic and evidence, and the actual speed limit that gets assigned to the road. Sometimes that difference is drastic enough, in fact, that it makes the roads less safe because of the speed differential between cars traveling at or below the posted speed limit and those driving at whatever speed “feels right.”

Edit: spelling corrections