That's a couple things:
1. Not based on any actual design criteria for the road
2. Assumes that 85% of drivers are somehow more knowledgeable than the engineers who are supposed to be designing our roads and transportation.
The claim that you should be always able to go 5-10mph above the limit seems to be a mythos invented in and ingrained in the fabric of the American psyche. Better approaches exist than to just pick a popularity consensus from a sample of random drivers in a study (who are predisposed to going faster, often because the study is done before full levels of traffic set in).
[0] https://www.strongtowns.org/journal/2020/7/24/understanding-...
I think you're misinterpreting the parent commenter. They said that, in the U.S., speed limits are almost universally slower than the natural (i.e. prevailing) speed of traffic by 5-10 MPH, and so everyone driving at the prevailing speed of traffic is inevitably exceeding the posted speed limit by a bit.
That is definitely true, at least if you're not in the rightmost lane of traffic sandwiched between semis and box trucks. 75-80 MPH in 70 MPH zones is common, and it's not unusual to see people driving 85+ MPH.
As an observation I'd agree. However, my impression of the parent commenter was that they implied that 5-10mph over the speed limit is the correct way to drive. Were that true, why wouldn't we just set the limit anyways? How did that limit get chosen?
Again, this goes back to the 85th percentile - the ways in which we decide how fast to go on a road or street are wrong. Of course, there's two things going on in this thread:
- Using tech to warn / limit drivers from being able to speed over an agreed upon limit.
- Engineering our roads so that the intended speed matches the prevailing speed of traffic.
Now I'm more in the second camp on this one than the first, I'll admit, but I don't think that we should just sit by and accept "some people speed, therefore we should all go faster" as a given. I have definitely witnessed people going 85+ MPH, especially if you're on an interstate far away from any city. However, this is not the norm and not really where the tech in TFA is going to be deployed.
Either way, the issue I take is with moralizing going faster than the speed limit. You might say it's the flow of traffic, but that just smells like justifying something that most drivers already want to do (go faster), instead of understanding the action (speeding) and its effect on the environment around us (increased danger, increased fuel consumption, increased noise pollution, etc).
Or you know, cars will just go the speed limit, 10 years from now and you won't even remember your brain simulated a shitty PID controller to hit some speed number subject to your irrational whims.
I suppose if the end result was that speed limits got adjusted up 5-10 mph to match the speed of the road it would be fine. I doubt this would happen in general, and I know it wouldn't happen universally.
