Introduce a Speed Maximum

I'm a bit concerned about the long-term effects of this plan (especially after laws formally change to disregard the old 'speed limit' signs entirely but strictly enforce the 'max' ones).

I believe that many current speed limits are much slower than the correct speed to drive at, and I don't think this is particularly controversial.  (I have driven on a perfectly straight, almost-empty six-lane freeway with a posted speed limit of 55).

This did not happen by random chance!  Aliens did not land and subtract 10 from every speed limit sign!  Existing pressures - revenue pressures from tickets?  political pressure from people who don't like cars driving fast by their house? - lead to speed limits being set too low.

If you switch to this new approach, in the absence of some reason to expect that not to happen again, I'd imagine that once your 'max' signs are the limit they will also be set too low.

In the UK there is a non-binding but generally observed rule that speed cameras allow you to drive 10% + 2mph above the speed limit(e.g. 35mph in a 30mph zone) before they activate.

This is a bit more of a fudge but better than nothing.

If we were to replace speed limit signs, it might be better to go all out and install variable speed limit signs. It's common to see people failing to adjust their speed sufficiently in poor conditions. A few days ago, there was a 35-vehicle pileup with two fatalities in California due to fog.

It gets people used to ignoring laws, 

I wonder if this is a good thing though? The greatest horrors ever committed in the world have been done by people following the laws and orders governments set out for them.  Having an obviously insane law that people experience on a daily basis might encourage some critical thinking about which laws are reasonable and which are not. 

Hard to test one way or the other but I still here people saying "It's against the law" as a self-evident reason not to do something far more often than I am comfortable with. 

People are not ignoring laws, they’re recognizing the limits of precise measurement, and understanding that the enforcement of the law is part of the crafting of the law. People do drive much more slowly in a 25mph than in a 55mph zone, and they’re punished differently for driving 90 on each.

It’s important to realize that the limits are set with the knowledge that it’s very hard to reliably (aka: court-upheld) measure small variations, so legislatures EXPECT it to be more of a nudge than a strict bright line.

But we, as a society, are annoying and will abuse a system that acknowledges this, so it doesn’t get written down that way, it just evolves into an equilibrium that most people just expect and live with.

I cannot recall having seen any recently but do recall seeing minimum speed limits posted on highways in the USA. That is sort of in line with your suggestion. 

I do think there are a number of aspect that matter with both setting speed limits, enforcing speed limits and driver's actually driving at some given speed. The two main aspects for me would be coordination among the drivers and congestion on the road. Both will have some connection to driver reaction time and vehicle capability (can the car physically change coarse, stop or accelerate assuming the driver has time to react).

Most of that is really situation dependent and even the speed range approach or some set max speed is a poor metric for defining some optimal rule. I sometimes wonder if fewer accidents might occur if outside certain areas (school/hospital zones, residential streets where lots of kids might be playing and the like) no speed was posted. Just have better liability assignment to those not driving at reasonable speeds. (Problematic from a practical perspective but not impossible given "blackbox" recorders and GPS data in cars and simple force analysis of the car(s) involved in any accidents.)  A concern here might be that even if we see a reduced frequency of events (seems to be somewhat supported by cases where towns/cities removed stop lights and people started viewing the intersections as if they were 4 way stops -- i.e., no one just assumed they had some right of way over the others.) A potential reasons this might not be a good idea would be if frequency declines but the when things go wrong they go very wrong -- never have fender benders but cars are totaled and people always crippled or killed would not be an improvement.

But I do think driving habits related to speed seem to be driven more by what would be a common law type process than the statutory "posted speed" law.

Note that in many countries, the rules or fines may be different for cars and trucks/busses.

It gets people used to ignoring laws

Wishful thinking. Breaking speed limits does not in fact gradually turn people into anarchists: most people continue to obey (and worse, respect) the laws that are actually enforced. 

Based on the title, I thought you were going to go another direction. But isn't it insane that a typical consumer car is capable of driving significantly over 100mph? In large parts of the country, there's nowhere that it's legal to drive anywhere near that fast, and an ordinary driver will never have a legitimate reason to drive that speed. I understand why this hasn't happened, but wouldn't it also be better if normal cars just weren't capable of going over, say, 90mph?

Where I live, I don't see many people going 15 over. I see most people going within -3 to +9 of the speed limit. They're following the law -- maybe not strictly as written, but as socially understood. There are a few people breaking the law -- and they get ticketed, etc. There are places where the speed limit is unreasonably low, and gets ignored (e.g. speed limit drops from 75 to 55 for construction zone, but no construction activity is visible), but in general, people around here follow the speed limit -- as socially understood.

The social definition is that +9 is OK, and it is logically based. Speed limits are only given to the nearest 5 MPH, so arguably (not legally arguably, but in people's heads) going 4 MPH over is not really speeding. Then, you need some kind of reasonable cushion. It defies common sense (but not the law) that a certain speed is perfectly legal in a variety of reasonable conditions, but 1 MPH faster than that is a crime. So, you have to have reasonable padding, say one 5 MPH increment. Thus, if you're going within 9 MPH of the speed limit, you're not speeding, just bending the speed limit, pushing into that safety margin.

Bumping a speed limit from the current value of 55 (+ social tolerance) to 65 (no tolerance) would not work. It would quickly become 65 (+ social tolerance), because you have not addressed the arbitrary nature of the speed limit. With strict enforcement, you could reduce the social tolerance value (I believe it was smaller before the 1970s national speed limit of 55 fostered widespread disrespect for speed limits), but it would difficult to eliminate it.

I doubt that speed limits are helpful at all. The sections of the German Autobahn with no speed limit (roughly 70%) have half the mortality rate per distance traveled of American highways^[1]. Granted, the average American driver is probably worse than the average German Autobahn driver but hey.

How about instead of doing some random proposed change with speed limit maximums and what not we do some AB testing and figure out what's safer?

Of course safety concerns don't exist in a vacuum. Every second we save on the highway by going fast is another second of life we get to spend doing something actually enjoyable.

One of the problems here is that our measurements are not precise (both in-car measurements the driver can see, and even more so for the outside law enforcement measurements). Especially when we take into account that cars don't have to be on cruise control, and often are not on cruise control.

That's why it is also assumed that if one is close to the speed limit, there is more room for doubt.

Fines, actually, do tend to increase gradually in many US jurisdictions, but insurance points (which often tend to cost way more than fines) tend to have sharp step-wise increases (and plea-bargains are done around those insurance point thresholds, reflecting the measurement uncertainty once again). Your MAX does roughly correspond to the first increase from the minimal number of insurance points for speeding to the next level of insurance points.

I think that you are correct, policies that "everyone knows" aren't "real" tend to reduce the degree to which everyone takes other policies seriously.  But I think a lot of the "unreal" policies are in place for reasons of liability, risk management, or other communication tool.  Also, seldom are any policy actually absolute or meant to be absolute.  Just ask your lawyer, nearly everything in life is negotiable.

What's more, speed limit policy is geared towards a complex set of goals, politically decided upon in a risk-managed, engineered way.  Then voted on by a board of people who might somewhat understand the problem.

You know what is almost never discussed explicitly in politics.  "What are our goals here?" and "What tradeoffs do we suspect these different decisions entail?"  Making this explicit, and letting people vote on politicians based on all this lucidity would be great, but reading, say, Thomas Schelling, I think it is also utterly impossible.

So we bluff speed limits (and nearly everything), and negotiate about it later.