The CA proposal is sort of a nothingburger that makes good headlines. There is no actually attempt to determine the local speed limit. It's just calling for 80mph governors. Like the ones certain company vehicles already have, that limit max speed. It's not a crazy idea and cars already have speed governors in the ECU's...the value depends on the car; Japanese cars seem to like 110mph. CA is just saying it should be lower, like 80. The highest speed limit in the state of CA is 70mph, so I guess they figure 80mph gives enough room for passing or whatever. It wouldn't do anything for speeding on lower - speed roads, but it would prevent the kind of extreme speeding you see in high speed chases or daredevil incidents. Or even mysterious events like that car that drove into the toll bridge at like 100+mph in NY... I always figured that was either a suicide or medical emergency.
One does wonder what happens if people buy a car in California and then go to Idaho or TX where they have 80 or 85mph speed limits. So it doesn't seem very well thought-out, like a lot of junk that comes out of CA.
They 80mph governor doesn't even seem that impactful because that type of highway speeding causes pretty spectacular crashes when they happen, but I think a lot of the road carnage is happening on urban and peri-urban arterials with lower speed limits, where people systematically speed.
There are systems out there that CAN use map data to limit speed by location, and the systems are already mandatory in EU countries, since 2022. They usually just display the current speed limit and beep at you if you speed, but they are advisory and can always be overridden IME. I can say it's kinda nice to have the speed limit always display in the dash along with your actual speed.
I know too much about speed limits because I'm on one of my road department's advisory committees. Most road departments consider the speed limit to be a property of the road, not something that you can optionally choose by policy. Speed limits are supposed to be set by the 85th percentile of speed that drivers naturally drive on that road, when there is no traffic. Under this system, the speed limit gives the driver some kind of real information about the road ahead. The road departments usually don't want to lower the speed limit for other concerns, like noise or not killing children (if they die it's just their fault). And besides, people ignore speed limit signs anyway, so there is a logic to this 85th percentile system. If you go around randomly lowering speed limits for other reasons, like because the neighborhood complained, the idea is drivers will catch onto this after seeing a bunch of 25mph roads that you can easily drive 40mph on, and they will start ignoring speed limits, and then when they go on a road that's actually a real "85th percentile" 25mph road, they will ignore the speed limit, assume they can get away with going 40, and crash.
Instead, if you want to lower the road speed because of noise, not killing children, etc., what you are supposed to do is redesign the road to a 25mph standard, and then people actually will naturally go 25mph according to the 85th percentile doctrine. You narrow the lanes to 9ft, put in curves, islands, or speed bumps, plant trees near the side of the road, in other words, design it appropriately, and wala, you have an actual 25mph road, which people who ignore the speed limit actually go 25mph on, and you also maintain the 85th percentile "speed limit is X and we mean it" doctrine. The problem is that re-designing roads is expensive. And road departments are very un-intelligent (I struggle to think of a discipline I respect less). The result is lots of roads have already been built going through residential or urban areas that probably are 30mph, but are built to 40 or 50mph standards, where people are tired of the noise, tired of speeders, and/or tired of sacrificing children on the altar of car culture, and they want to drop the speed limit but the road departments 1) won't let them without redesigning the road and 2) can't afford to redesign the road. If enough children die in one place, then sometimes they will do something. Sometimes. But then they fail to make those same design changes elsewhere, at least until enough blood has flowed.
