On the one hand, I'm against tracking everyone, everywhere. On the other hand, I'm totally for ALPRs dispensing indiscriminate justice on people violating speed limits. I wish we could have auditable, trustworthy ALPR boxes that only report speed violations to be immediately turned into tickets, and don't store license plate numbers of people who follow the law.
Red-light cameras in the US opened up all sorts of issues nobody thought about when they were just "totally for" ticketing people who ran red lights. We got issues like local governments tinkering with timing of traffic lights in order to increase the number of violations, because violations are lucrative and who wants to defend red-light runners? People who run red lights are bad people who do dangerous things, and they should be punished!
There are also the ongoing studies into whether red-light cameras actually increase collisions, by incentivizing people to stop unsafely.
And that's without getting into the due-process issues, or the way offenses start creeping into more expensive categories (see California cities which have been "upcoding" various other offenses, like rolling turns, into full-on red-light violations in order to collect larger fines).
Speed limits have a number of notorious issues; they tend to be set for political, rather than safety, reasons, and very few US jurisdictions actually follow the general best practice of setting limits based on 85th-percentile speeds. Some smaller towns infamously derive almost all of their municipal budget from running speed traps (i.e., a 55mph highway passes by, the town annexes a tiny strip of it and sets a far lower temporary limit, then tickets as many unsuspecting drivers as possible). What you're asking for is to industrialize all of those issues.
You'd like to invoke Florida Man, but plenty of small jurisdictions rely on the income stream from fines. Ferguson, MO comes to mind. The police fleecing blacks and out-of-towners, it does wonders for the perception of the law.
Without fail, whenever I approach one of those intersections on a green light where the pedestrian signal has changed to a flashing hand, at least one car slows down.
I have seen people stop at a green light where the pedestrian signal is a solid hand (meaning the light will change to yellow soon).
Acting in an unexpected way is a recipe for an accident.
I also am not comfortable calling the "85th percentile" rule a best practice. Seems like a moving target that has more to do with perceived safety than actual safety. Here's someone else's take: https://www.strongtowns.org/journal/2018/1/25/speed-kills-so...
Much of what you're trying to do is impose one-size-fits-all enforcement on both types. Controlled-access roads forbid pedestrians and bicycles, so arguments about protecting pedestrians and bicyclists on those roads fall flat. They should be using 85th-percentile metrics, in combination with the known design speed of the road, to set limits. But because controlled-access roads tend to have higher speeds, they're also the most tempting targets on which to run speed traps (i.e., if you can set a stretch of road to 25mph when the rest of it is 55mph, and park a hidden camera or cop right at the boundary, you can make a lot of money for your municipal budget, and precisely zero dollars of it will have been justified by increased "safety").
For the non-controlled-access roads, most of the real solutions the strongtowns/walkable/bikable/etc. movements want are going to come down to radically different infrastructure which have nothing whatsoever to do with speed limits. Speed limits are at best a non sequitur there.
I don't think the 85th percentile rule is entirely bad, just not a "best practice", which sounds to me like "one-size-fits-all". The Strong Towns post I linked to said it makes sense for highways as I recall, which seems perfectly consistent with what you wrote.
Anyway, to reiterate, I am still interested in knowing how frequently speed cameras and the like are used poorly. The only uses of speed cameras that come to mind in my experience were not on "controlled-access" roads and seem justified to me. In fact, I rode my bike several times on one road with a speed camera that many drivers whined about back when I lived on the east coast. It was not uncommon for people to drive 15 mph or more over the speed limit there, despite the pedestrians. If I recall correctly the speed camera was added before a pedestrian crossing.
Edit: What I am recalling was actually multiple cameras on multiple roads. http://www.gazette.net/stories/12092010/laurnew185647_32536....
What is this metric supposed to imply though? We obviously have roads with limits above 30mph already, so clearly decisions aren't made based on merely chance-of-death-assuming-a-collision being too high.
So the figure shows that if there are more pedestrians likely to get in the way of your car then you should drive more slowly if you care about not killing those people.
When the figures regress to mean next year or two it's taken as proof the new limit was correct. So we slowly deviate from the 85th percentile rule, and get weird stretches of dual carriageway at 30 or 40 with a speed camera in the middle.
Driving 50% over the limit is dangerous, fining people for going 2mph over is just "creating revenue".
This makes no sense. Source?
Besides, 30 kmh limit is exceedingly common in European cities.
A lot of the city has been reduce to 30km/h (18.5 mph) zones which drivers hate but makes it a lot safer for pedestrians.
[1] https://www.watson.ch/schweiz/strasse/861871246-in-welchen-s...
One principal difference is Swiss traffic controls, at least in French-speaking parts, is that they prevent intersections of traffic flows. E.g. you can't turn left on a green that allows going straight unless cars in the opposite direction are held by the red. That is, if you are following the signs and lights, you will simply not have a chance to run into another car going in some other direction.
Not sure how things are in the States but over here in Eastern Europe there are lots and lots of stupid speed limit signs, I call them "stupid" because if you were to follow them literally (instead of going with the traffic flow) then most probably you'd cause accidents for being an obstacle on the road.