Is Every Speed Limit Too Low?
priceonomics.com
priceonomics.com
Results show that the average risk of severe injury for a pedestrian struck by a vehicle reaches 10% at an impact speed of 16 mph, 25% at 23 mph, 50% at 31 mph, 75% at 39 mph, and 90% at 46 mph. The average risk of death for a pedestrian reaches 10% at an impact speed of 23 mph, 25% at 32 mph, 50% at 42 mph, 75% at 50 mph, and 90% at 58 mph. Risks vary significantly by age. For example, the average risk of severe injury or death for a 70‐year‐old pedestrian struck by a car travelling at 25 mph is similar to the risk for a 30‐year‐old pedestrian struck at 35 mph. https://www.aaafoundation.org/sites/default/files/2011Pedest...
Please think of everyone on the roads, not just drivers, when making arguments like these.
> Luckily, there is some logic to the speed people choose other than the need for speed. The speed drivers choose is not based on laws or street signs, but the weather, number of intersections, presence of pedestrians and curves, and all the other information that factors into the principle, as Lt. Megge puts it, that “no one I know who gets into their car wants to crash.”
Rather than speed limits, we need to look at other avenues to reduce pedestrian traffic deaths. Just shooting from the hip, I think that we could do more to communicate to drivers the presence of pedestrians, and to make sure that rural highways and boulevards have shoulders or sidewalks for pedestrians.
A more complete analysis of pedestrian deaths: http://www.popcenter.org/problems/pedestrian_injuries/
Here are some useful factoids:
- Finally, the more one drinks, the higher the risk of being involved in a pedestrian-vehicle crash resulting in a fatality. One study found that out of 176 pedestrian fatalities, 86 of those involved pedestrians who had been drinking, nearly all of whom had BACs of 0.10 percent or more. - In addition, the same study noted that 71 percent of all fatal pedestrian-vehicle crashes in the United States in 2000 occurred in urban areas. - Finally, the majority of pedestrian injuries and fatalities happen to males between the ages of 25 and 44.
This gives us a pretty targeted demographic! Start a "dangers of the road" campaign targeted at pedestrians who are men, aged 25-44, drink at night and who live in rural areas.
> “I don’t want to lie to people,” Lt. Megge tells us. It may make parents feel better if the speed limit on their street is 25 mph instead of 35 mph, but that sign won’t make people drive any slower. Megge prefers speed limits that both allow people to drive at a safe speed legally, and that realistically reflect traffic speeds. People shouldn’t have a false sense of safety around roads, he says.
> If people and politicians do want to reduce road speeds to improve safety, or make cities more pedestrian friendly, Megge says “there are a lot of other things you can do from an engineering standpoint.” Cities can reduce the number of lanes, change the parking situation, create wider bike paths, and so on. It’s more expensive, but unlike changing the number on a sign, it’s effective.
Read the article before commenting, people.
Everyone knows a place cops like to hang out, and slows down accordingly.
Why not enforce speed limits more frequently so people obey them? Why suggest a worse solution (encouraging all drivers to go faster) instead of punishing more people for driving irresponsibly?
Place speed camera every 100 meters and red camera at every cross (without cheating the yellow, which is a separate problem) and watch dead rate drop.
People are notoriously bad at assesting danger and probability. Them driving faster doesn't make the faster speed always reasonable.
Ticket them and make money for the municipality. Don't engineer new solutions that cost tax payers money and make rodes less safe for people not in cars.
http://www.nydailynews.com/new-york/nyc-crime/exclusive-spee...
I have to say, this article simply is not rigorous.
I've seen it argued that shoulders/sidewalks actually make roads more dangerous, because drivers drive faster when they're present.
> This gives us a pretty targeted demographic! Start a "dangers of the road" campaign targeted at pedestrians who are men, aged 25-44, drink at night and who live in rural areas.
Isn't that classic victim-blaming? Getting pedestrians off the road would reduce pedestrian deaths, but it's the wrong way to solve it as a matter of principle.
Sounds plausible, I'd love to know the context. Got a link?
As for the victim-blaming... Teaching safety isn't something that should be controversial. If it's victim-blaming to teach our children to look both ways before crossing the street, then I'm ready to throw American culture into the garbage.
If you're dead or severely injured, what does it matter if it was not legally your fault? I pay attention to other cars regardless of whether I have the right-of-way or not. This has saved me from accidents. I don't care to be "dead" right.
I don't understand pedestrians and bikers who wander carelessly into traffic, presuming that having the right-of-way is some magic shield against getting run over.
It depends on a lot of factors. The presence of a separated sidewalk might imply a hard separation between vehicular and pedestrian traffic which can increase speeds. Deliberately blurring those boundaries, as is often done in small European cities, makes the road more ambiguous and this leads to slower, more cautious drivers.
Confidence equals speed. Long, straight, wide roads with ample room for stopping encourage people to drive faster. Narrow, winding, difficult to navigate roads are naturally approached with more caution. The trend has been to straighten out and widen narrow roads, to eliminate any impediments to "traffic flow", which often makes for roads over-engineered for their intended speeds.
The presence of a sidewalk doesn't make people drive faster, but the philosophy of separation of traffic flows that leads to sidewalks being used does.
Think you may be mixing up two words
> In addition, the same study noted that 71 percent of all fatal pedestrian-vehicle crashes in the United States in 2000 occurred in __urban__ areas
The problem is that enforcement of such a rule is impractical in most situations. If you're going 35Mph in what was once posted as a 25Mph zone, and it was posted as 25Mph because there's a school zone in two blocks, even if there's a strong argument that 25Mph is the objectively safest limit, you'll then have to prove that the driver knew there was a school in two blocks. Then the driver could argue school was out. Etc, etc, etc.
There's a tension between administrative efficiency regarding enforcement and fairness to the accused. This tension is made greater the larger the community. In a tiny community everybody can trust the sheriff to make a judgment call, and the ticketed person not to contest the issue. As the community becomes more diverse and less personally connected, and the environment more complex, you need to rely on strict, clearly articulated rules that minimize discretion.
There's another axis we're dealing with here, too. Do we emphasize overall outcomes, or do we emphasize individual justice (for victims, for offenders)? If you emphasize overall outcomes then we focus on prevention and social measures. If you emphasize individual justice you want to make it easier to punish offenders, as well as make the rules clear so that everybody knows precisely how to avoid offending.
I tend to emphasize more on overall outcomes. I think most people do, at least in the abstract. But the moment a kid or a biker is run over many people switch into individual justice mode, and that's how elections play out.
The roads there are twisty, with dry stone walls either side, mostly. Except for the mountain roads that are spectacular.
Then there's the TT, when bikers from all over the world come there to race, and about a dozen or so die each year. Apart from that, though, road fatalities are not exceptional.
Driving there is great, because you don't have the constant worry of "am I going over the limit?" or "what is the limit here?". You stop worrying about the number, or checking your speedo, and concentrate on driving safely on the road. How fast or slow you're going becomes irrelevant, it's all about how you drive on the road you're given.
The speed limit is as much a target as a limit. If the limit is 60 then there's a feeling that "well, they know their business, it must be safe to drive at 60 here". What is authorised becomes advised. No-one can blame you if you lose control due to speed, because you were driving under the speed limit so it must have been OK.
With no limits, it becomes your responsibility to decide what's safe. And yes, there are people who think they can drive safely much faster than they actually can. But they they tend to head for the mountain roads where's less traffic to get in their way. There's also less macho bullshit around it because there's no "rebel cred" in driving over the limit when there is no limit.
Conversely, driving slowly in town is accepted, because it's clearly done for good reasons. Speeding in town isn't socially acceptable (if you want to go fast, head to the mountain and do your worst). People drive more safely, and more courteously because they have responsibility.
It's a great system. I wish we adopted it here in Australia.
Why do you even need cars there? Everything is within cycling distance.
Nowadays, I ignore any speed limits. I'm frequently speeding when it's safe, and I'm very frequently going slow enough to people flash lights or honk at me - no crashes since that.
I of course recognise I was at fault and don't blame the speed limit - I should've known to adjust my driving regardless of the limit. However this way of thinking isn't uncommon and while the speed limit isn't at fault, it had its part in causing the crash.
It would be unreasonable (& annoying) to have different speed limits for every different corner/stretch of road. There's also considerations such as the weather & lighting conditions to take into account (& while I have seen signs on motorways for variable speed limits based on those in Europe, you cannot expect every case to be covered).
I seriously doubt this. It's a speed 'limit' not a speed 'target'. I can't fathom how you could think 'sign says x, I'm sure if I go that speed I can get around this sharp turn safely'. How strict were the driving tests where you learned?
Public transport is good, though.
1. How not to do it IMO: Road next to me had a limit of 60 because of "road works", there even was a road works sign standing there. Everyone knew it was safe to drive 80.
One day I was driving suddenly after months of inactivity a worker comes walking out into the road while I come driving. The sun was low and I just saw his legs moving and managed to brake and steer away.
If I had crashed it would have been my fault - and I would have deserved jail and losing my license. But I totally wouldn't say road authorities would have been without blame:
Designing a 80 zone, then training everyone to think the road works sign is just a forgotten artifact is really really not a good idea if you intend to suddenly send your people out there in low light.
2. How it should be done IMO: Next to a school that I sometimes drive past there is a 60 zone. But it (used to) only apply when kids could be reasonably expected to be there (0600 - 2000 or something). Every summer road authorities would even cross it out.
This way we are constantly reminded about why there is a very valid reason to slow down at this place - and we are reminded that at least some of them honestly think before they restrict us.
"Authorities consider this road safe for average drivers at x mph, therefore it must be safe for me at x * 1.y".
The y in the "1.y" pseudomath btw is proof enough to me that claims about enforcement not working are wrong: when you cross state borders it is easy to witness considerable changes in "typical y", the amount of relative speeding customary in the local population of drivers. Road design certainly has an influence on actual speed, but so do limits and enforcement.
Studies [1] have shown that not to be the case.
It always amazes me how cars commercials show awesome dashboards with 250 mph speedos, perfectly knowing there is no single road that you can lawfully go that fast.
Heck, it probably won't cost much more than a thumb drive to stick into your car computer port to update speed limits built in.
Except in most places, neither is happening. People are driving dramatically over the speed limit because that is the natural speed of the road, and no attempts to change the actual speeds of traffic are happening because they cost money.
So people get to die for the multitude of reasons the article outlines because of political deadlock.
Given the stated stated observation that speed limit signs have very little correlation with driver behavior, the only way to significantly impact road speeds is through road design.
I vaguely recall that the US interstate system was generally designed for 150-200 km/hr.
It seems like it would compared to a wild west situation where everyone is doing lots of drugs/going as fast as possible, but in our current society cracking down further offers no further benefits and may come at additional costs.
For example:
Automatic breaking technology on cars that can detect people who the driver might not be able to see (child running out from in-between parked cars).
Better selective enforcement of speed limits so that people pay a bit more attention. When an empty country road says 25mph due to a speed trap, it reduces the trust people place in speed limits, meaning they won't respect the 25mph speed limit as much even when it is in a school zone where children are constantly crossing the street.
Better side walk design. I shouldn't be only two feet from a speeding 2 ton object even when everyone is following the law correctly. Having space between the road and sidewalk helps. Maybe add some trees and other objects that will stop a drunk driver who runs off the road.
Bike paths for those riding bikes. Also separated from the road.
I'd rather figure out how to make city drivers more attentive and responsible than effectively turn every arterial road into a mini highway.
I'll stop you right there.
We are talking about how to prevent accidents, not how to make them less serious.
I have often heard cited, the fact that force scales with acceleration in a non-linear way, as the reason for speed limits. That is not the case, nor should it be.
These roads are not just for fast driving cars.
To try to counteract this, those signs that tell you your speed were put up that blink when you are going over the limit. They were promptly ignored.
So really I'm just trying to reiterate that what the article says is absolutely true - people will drive what they feel comfortable going, not what the posted speed limit says. In practice, the risks are there, but nowadays everyone knows to avoid main street for pedestrian crossing because its approaching highway speeds now. But on very congested roads like our main street (this being a 250 year old town, where there is no traffic shaping planned, so all through traffic goes down the road that also has the most foot traffic) you aren't going to have an easy answer, because slowing down traffic can be just as dangerous when its bumper to bumper for the ~5 mile long road through town and drivers will go mad being forced back to 25mph combined with the immense traffic bottleneck it would reintroduce (the main reason they fast tracked paving the road in the first place - traffic would back up onto the nearby highway offramp because of how bad main street traffic is).
I think the reality is that busy streets are just never safe for pedestrians (or bikes, etc). That is why you invest in crosswalks meant to funnel people across them all at once, in centralized places, where traffic is already forced to stop. And if you really care, you get the cars out of downtown entirely.
I have cycled routinely on roads with speed limits greater than this. The first that comes to mind is Madison Ave in Sacramento (often 50mph+). For that matter I used to have a commute that took me on a brief stretch of I-5 in San Diego - that was hair-raising, to say the least. It's legal there due to lack of other options.
The speed limit is supposed to be the upper bound. By over using low speed limits, we indirectly increase the danger level for vulnerable road users because of the reasons detailed above.
and this should come together with ban of cars older than 10-15 years not meeting current safety standards and of course all cars should be checked for quality of their brakes and other parts before being allowed to drive
We have several cities, but they're somewhat small by comparison to some of the places a lot of HN readers are from. There's no analog to SF/Silicon Valley here. Sure, people walk around Detroit, but for the most part, that's down-town in a few select areas (yes, people do walk in the outskirts, as well, but there are much larger dangers going on there than pedestrian fatalities). There are several other cities where there is a lot of walking traffic. The speed limits are 25MPH in all of the places you'd expect them to be[0]. The 85th percentile rule does not apply in these cases nor does it apply on residential roads. I live on a main subdivision road and folks commonly exceed 25MPH. I call the cops when I see it and they've had patrols going on in my neighborhood every day for the last two weeks (it's very profitable for them). People are finally slowing down again. You will get pulled over for going 5MPH over the limit in these situations, whereas that would never happen on a main road unless you were doing something else wrong.
I'm a huge supporter of the 85th percentile rule, but only when applied outside of these cases. Yes, people walk on the county/state roads that are set by this rule, but there are proper signals with increased delay times when pedestrians push the magic button (which, on these roads, actually does something -- the walk/don't walk signals won't turn to walk ... ever ... if the button isn't pressed). On freeways, there's no pedestrian traffic (on purpose, anyway).
[0] My daughter is hard of hearing (with hearing aids and all) and ADHD. She's the kid who's going to chase a ball into the road without looking and not have strong enough hearing to notice a car before it's too late (she rarely wears the hearing aids at play outside to fear of damaging them). I have followed kids home in my car and had discussions with their parents about their driving. I stick with the rule of "keep up with traffic" and will speed when that's how fast everyone else is going, but I never exceed the speed limit in pedestrian areas and I hope most adults follow suit ... though if my neighborhood is any indication, the worst time for speeding is when parents are heading to the Elementary school (located in my neighborhood!) to pick up their children. They'll blow past the crossing guards while kids are walking home from school doing 40 MPH. I guess if it's not their kid on side-walk, some folks feel it's more important to get where their going.
A low speed limit typically is enforced with a traffic camera. Additionally we've go a lot of dynamic speed signs which show a speed limit which fits the current traffic conditions. (empty road at night - it's turned off. Rush hour - 80 km/h. Fog - 60 km/h And several steps in between)
Not having a "fixed" all the time limit makes drives accept the speed limit more easily.
Oh yes, and 85'th percentile. I frequently drive "+15km/h", so I go 95 when there's 80 allowed because the fine when I get caught that is not too expensive. (Fines for speeding are lower when you get caught outside city limits, speeding in a residential zone or in front of a school for example is one thing I have no tolerance for as well.)
When you accelerate from the 80kmph to the 140kmph you better have a good engine or you feel stressed like hell slowing everybody else down.
And keeping right all the times just creates a lot of unnecessary dynamics in traffic flow.
Don't even get me started on congestions when everybody slams their breaks and hit the warning blinkers.
German traffic is for macho wannabe race drivers.
I rather have US traffic or the traffic in the Netherlands where everybody just set their cruise control and drive casually.
In the Netherlands they also have trajectory speed checks, so you cannot speed anywhere from point A to B, since they clock your total time. Works wonders for getting a nice steady flow on the highway.
My 5 cents anyway.
The article talks about differential speed and lane discipline. In Germany, it's not rare to see people driving 250 km/h (155 mph), but some heavy trucks are restricted to 80 km/h (50 mph) regardless of the speed limit. Germans are very strict about lane discipline though. It's generally illegal to pass on the right or be in the left lane when not passing, and someone who puts their turn signal on to move left will usually respond to a flash of the headlights from an approaching car and wait for it to go by.
As an American who has spent a lot of time in Germany, and driven across Texas a few times, I sometimes wish for German style speed unlimited-speed highways in the US, but I think it would be hard to get American drivers to adopt German attentiveness and discipline.
1) The "priority road" system, indicated with diamond signs, for right of way on secondary roads. This isn't quite as weird for outsiders as the weird British Columbia flashing green lights thing (wtf), but still, almost caused an accident the first time I encountered it at night.
2) When traffic is stopped and you want to allow emergency vehicles, you make a gap between (California) lanes 1 and 2, i.e. where Californian motorcycles go; in the US (and everywhere else I've seen), emergency vehicle drive on the shoulder. Either makes sense, but knowing what's going to happen is good. I naturally pulled toward the right in the leftmost lane until I looked behind me and saw flashing lights coming up fast.
I'd say in the UK it's pretty similar as well. The standard limit on single-carriageway roads, unless indicated, is 60mph/97kmh. This could be anything from a bypass around a town, to a small country road with tight bends and steep drops at the side.
The limit is usually only lowered if going through a town/village (typically 30mph or 40mph) or if there is a some sort of danger that you wouldn't expect, like a hidden junction on a bend.
As far as I can see those limits exist to make the politicians responsible for them look concerned about safety.
> Rush hour - 80 km/h
Does "rush hour" mean something different in Germany? You couldn't go 80 km/h in rush hour if you tried.
Is it possible you live in NRW? It's a bit extreme there. Much fewer speed cameras in other parts of the country.
A poorly enforced law provides a tool for executives (the law enforcers) to legislate (make their own laws) without any say from the real legislators. It's a loophole of sorts in the US's separation of powers.
Take marijuana. It's illegal to smoke marijuana. It's not illegal to be black. Yet the selective enforcement of the marijuana law allows authorities in any given district to shape policy on race without ever having to explicitly put a law on the books.
This is why the Computer Fraud and Abuse Act is so dangerous. It is broad enough to be used as a tool to enforce laws that would be too unpopular to explicitly pass.
It's also why threats from the US government to "ban encryption" should not be taken idly. You think to yourself, "Certainly they couldn't ban encryption, nothing would work without it." But they wouldn't enforce it across the board, only selectively.
I remember reading a story of a multi-billion dollar corporation in Russia being sold for pennies on the dollar, essentially at gunpoint. Otherwise, they'd prosecute it for being run illegally, since essentially all corporations are run illegally, because that's how Russia's legal system is set up.
Last I checked, encryption _is_ banned in the U.S., isn't it? So it's already the case that the government could selectively jail people for using encryption, as it sees fit.
The officers argument to my dad was "why would you go so much slower than traffic (this is on i78 in PA, mean traffic is around 75 and he was going the posted 55) if you aren't trying to hide something by going the speed limit" when the back of his covered pickup was full.
Turns out he was just bringing china plates to my grandparents.
He didn't get ticketed for it, but it gave the police a legal reason to pull him over beyond arbitrary suspicions.
The solution to this seems to be to make the roads designed for lower speeds, or to reduce the safety margin, or as other commenters suggest to add traffic calming measures. I'm pretty sure this would reduce traffic speeds, but I don't know if it would reduce traffic safety.
And as with pretty much any community that has that much value in their house, they're huge NIMBYs.
Cars are like bullets in our hands and should be handled with the utmost of care.
Edit: Forgot to add my favorite solution: Add a very high, hard speed limit (130mph?) on all streets, and let traffic signs serve as recommendations. Obviously, also limit to walking speed in neighborhoods where kids play in the streets, or city centers.
I don't trust their self-evaluation of their own skills.
Racing is dangerous and the people who do it know that they're taking a risk. It's not appropriate to take that risk when driving on a road.
The point of the article was that speed limits should be set to keep the most amount of people at the same speed. Otherwise by reducing them too much, you create environments where there are greater differences in speed between cars. That is what is dangerous, not the actual number itself.
Or come over to Germany sometime and enjoy some Autobahn driving with literally no speed limit whatsoever (on certain sections). Early Sunday morning (when trucks are banned) in a good car; that should be on those "N things you do before you die" - bucket lists.
At the other extreme, on neighborhood streets in residential areas, the rationale for the 85th percentile rule (reducing the speed differential between cars traveling in the same direction) is absurd: these speed differentials are much lower and much less important than other speed differentials. If a car driving down my street at 30mph has trouble dealing with a car going the same direction at 20mph, it will also have trouble with the kids playing basketball in the street, or the car headed the opposite direction without room to pass, or the car backing out of a driveway, or the bike going 15mph. Conflicts between drivers headed the same direction are a non-issue on these types of streets.
And there are streets in the middle. A major commercial street in my town is four very narrow lanes (the right lane is actually less wide than a city bus, so when a bus is traveling the same direction you must enter the oncoming lane if you try to pass), with very small blocks, crosswalks at every intersection, tons of pedestrians and cyclists, tons of cars turning left across traffic, etc. Should this be set at the 85th percentile speed? Although it's more debatable, again, I don't think that the speed differential between cars traveling the same direction is likely to be a major contributor to fatal accidents here--on a busy urban street like this the danger is much more likely to arise from the speed differential between pedestrians and cars, a car turning left and an oncoming car, cyclists and cars, etc.
Obviously this applies less to country roads where pedestrians are rarely encountered, speed limits are well over 40mph and drivers often should be paying more attention to the bends ahead of them than the notional speed limit when judging how fast to go anyway.
Accident rates are only a concern because of harms from accidents, including, most especially, fatalities.
* speed limits are set at the 85th percentile of speeds to minimize speed variance, giving slow drivers a target speed and thereby making them go faster than they might otherwise go (but still at a safe speed).
* larger variances in speeds correlate with both greater traffic and frustration. if highway patrol could enforce just one law, it should be that drivers should move to the right if they are not passing cars on the right. this allows faster cars to clear out of congestion, increasing the overall average speed and throughput for a given section of road. it also reduces overall frustration.
* traffic enforcement as a revenue generator creates a perverse incentive and adversarial relationship largely exacerbated by artificially low speed limits. let's abolish those limits and bad incentives and give the police more time to develop relationships within their community.
* change the term "speed limit" to "safe speed" on signs (along with commensurate fines/laws), because that would have the same normalizing effect on speed variance, while also removing the revenue incentives for police.
* distracted driving is the real killer on the roads, not speed. changing roads to make them more hazardous (like narrower lanes, obstructing sightlines) probably reduces distracted driving more than it reduces speeding (just my conjecture), and thereby lowering accidents. i don't mind narrower lanes and such, but i'd advocate separating cars from bikes and pedestrians as much as possible so that cars can still move at a good clip while providing greater safety for pedestrian and bike traffic.
Well that will never happen..
Obligatory Reference to wit: http://www.slate.com/blogs/the_world_/2014/08/29/will_everyo...
So... (1) maybe a welfare state isn't that bad? and (2) that's akin to not believing in small-scale trials/pilots because they're small.
I can understand saying "well they have a bunch of Oil money and not much ground to cover" but most things in the universe can be solved at scale in the same way they're tackled in these countries.
It'd be like if Sweden was the only place that invented spark plugs and you're like "Well they're a really small country so they have less people to give spark plugs to so it's feasible".
Bike riders also solve traffic jams (by NOT going bar car), make cities more silent and more liveable, bring more business to local stores and restaurants etc.
Similarly, the Nordic countries are not homogeneous: most of the population lives near their southern borders (on the Baltic Sea), while their northern areas are barely populated at all. It's very similar to Canada: most of the population there lives within 100 miles of the southern (US) border.
So you can't compare population densities like that: you have to focus on specific areas. What's the population density of Malmo versus Philly? Stockholm vs. DC? And even here it's hard to compare, because for instance "DC" could mean just the District itself, or it could mean the much larger metro area around it, and all parts that are reasonably commutable. Most of the "DC" population lives outside of DC.
Offhand, I'd say Sweden has substantially better public transportation because most of the population lives in a few large cities, and also because it's a better-managed country that invests more in infrastructure for the common good.
"The United States has terrible public transport" doesn't hold true for pocket regions which have very reliable public transport. You just can't very reliably go across the country because some of our states are larger than many, if not most, European countries. Not to mention geographical differences. Compare a topography map of Sweden with California.
And then: https://www.nhtsa.gov/press-releases/traffic-fatalities-shar...
Someone has a pretty big axe to grind when they have to lump speeders in with drunk drivers in order to get the statistics they need... I suspect that the number is almost the same even if you remove the non-drunk speeders from it. (I'm being a little snotty and disingenuous--I suspect that the issue is that the number of non-drunk, speeding fatalities is almost nil and that drunk and fatality almost always implies speeding as well).
And I still can't believe how many people die because they won't put on a bloody seat belt. Sheesh.
So, what we know is that using electronic devices in cars is more dangerous than speeding. So, we clearly need to remove the cellular towers near highways, right?
- suicides (somewhere between 10 % and 20 %) - spontaneous deaths (around 10 % of traffic deaths, driver dies of old age or similar; they are included in statistics even though the accident was not actually cause of death) - gross negligence (at least 30 %: the driver is severely drunk, does not have a license, the vehicle has not passed inspection and the driver is trying to escape the police at 160 km/h on a 50 km/h zone; sometimes you have all these at the same time!) - freak observation errors (at a rail crossing, just drive under the train)
Well, even then, the US still has somewhere around 3-4 times more deaths on the roads per capita than other western countries.
It would be interesting to know what the ratio of deaths per driving regularly capita is for all western countries.
Setting the limit at 80 doesn't make everyone drive 80, either.
Evidence, please.
We did this experiment and the evidence is against you.
Fatalities did not significantly increase for any of the states that increased their limits after the 55mph thing ended and there was some weak evidence that they went down.
And it's the large differentials in speed which create the most dangerous conditions and accidents.
Even rigorous enforcement can't catch everyone, and the high speeds quickly become the norm; with people going 65 the dangerous exceptions.
The current Swiss yearly deaths are around 250, a very significant drop from the typical 1000 I remember growing up in the 80s - http://www.oecd-ilibrary.org/docserver/download/7515011ec041... lists a maximum of 1720 in 1971. As the population increased about 25% in the same period, that's about an 8x drop in per-capita rate.
In the same period, US fatalities dropped from 52000 to 35000 (https://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_i...), for a per-capita drop of 2.3x (the per-mile drop is 4x, the current Swiss per-mile rate is 60% of the US one).
In the period I remember:
- speed limits were reduced in town from 60 to 50km/h, on highways from 100 to 80 km/h and on freeways from 130 to 120 km/h
- speed limit enforcement became much more pervasive (there's an automated radar every 10km or so on busy freeways?)
- cars got safer (this applies everywhere)
- drunk driving limits were reduced (and people's attitude to driving after drinking changed substantially)
So suggestions that speed limits are irrelevant and pointing to reduced death rates in the US as evidence are not very convincing when other countries saw substantially larger improvements over the same period.
I'm curious what per-capita driving hours and mileage changes look like over the same period.
You can see that this holds true when looking at some of the Eastern European countries that only recently got better road infrastructure. E.g in Poland, the max speed limit at a highway is 140 km/h, whereas countries like France or Spain keep lower limits (130 & 120 respectively).
I think that today, any highway limit below 140 km/h is just obsolete and should be revised. Now, I would prosecute harder those who speed in urban areas, where the risk of hitting pedestrians or cyclist is real.
2. Speed limits help maintain a steady flow of traffic.
My father found driving in France terrific because all lanes were limited to 130 km/h. Steady flow, no stress. In Germany, driving on the autobahn is stressful. The speed difference between the lanes is too big. From my experience, it is: right lane 100 km/h, middle lane 140 km /h, left lane “Get out of my way you sucker!!” >180 km/h. Passing someone on the middle lane means taking the left lane and accelerating as fast as possible because the next space ship SUV is coming closer at rocket speed. They tailgate you, sometimes flash lights or use their left blinker to bully you to switch lanes. Because of that, many people cut into the safety distance of the car they just barely passed to get rid of the bully.
The speed difference also causes backpropagating traffic jams. To the observer there is no obvious reason where the slowdown comes from. It was simply created by people driving too fast compared to the car in front of them, having to brake, causing the cars behind them to brake, etc.
Hence why distance to the car in front matters, proportionally to speed, not speed itself as an absolute metric. 180kph is not a definitive tailgating trigger when people behave. Case in point, in France people regularly tailgate you too even at 130kph, even more so because they feel safer due to the comparatively reduced speed.
> The speed difference also causes backpropagating traffic jams. [...] It was simply created by people driving too fast compared to the car in front of them, having to brake
It was created by people either braking too late and having too much of a tendency to tailgate you, or jumping out of their lane and sitting there, and it happens just as much in France. It's a property of reaction time and distance WRT speed, not speed itself.
> They tailgate you, sometimes flash lights or use their left blinker
I've mostly seen this behaviour when the car either cruises at a reduced speed on the left lane or irresponsibly takes over when it should have no business in doing so WRT current traffic: it's just as disrespectful to others to tailgate someone as it is to take over and block a lane when you're driving at a locked 140kph to overtake someone at 138kph and there's constant faster traffic on the left. I've also witnessed people playing vigilante and do this voluntarily precisely because of the existing speed limit.
My experience is that most issues on the road are a byproduct of terrible individualistic human behaviour, and setting limits on arbitrary metrics do not solve that.
I don't understand why this isn't mentioned in every speed limit discussion. Driving in Australia / New Zealand with very strict speed limit laws is so much more relaxing compared to the anarchic mess on German autobahn or the disobedient mentality of Czech roads...
They are also so that cars can get on the highway (some older cars or larger cars can't get to 140). Then you have trucks that have 80/90kph max. The differential gets large.
And then there is the issue of noise and particles in the air. Cars are most economic around 80kph.
At least these are reasons in the netherlands
- make roads narrower (either by optical illusion with narrower painted lanes or physically)
- reduce stretches of straight road: traffic circles are great at breaking up a straight line
- remove all straight lines from highways, making them perpetually in a slight curve. This is something that has been done in many place in Europe for newer highways. This breaks up the monotony of being on a straight stretch of highway and therefore feeling the need to drive faster. As an example, notice the slight curves in the limited access highway (A5) and compare to the 2-lane road that runs parallel to it (D605) in segments of straight lines:
https://www.google.com/maps/place/A5,+France/@48.4802471,2.7...
The government recently increased the speed limit on a long highway I take a few times a year. Honestly a lot of people were driving at or below the limit and I felt no reason to speed. The highway also seemed to move better and felt a lot safer with fewer lane changes needed.
But it seems wrongheaded to focus on 85/15 out of safety, in areas where the safety concerns are for surrounding property, bikers, and pedestrians. I'd love to see more emphasis on designing roads for intended speed limits.
Communities need to enforce zoning that makes certain areas (malls, downtown, etc.) pedestrian areas only. Additionally, separate bicycle traffic onto different paths.
That would probably increase safety quite a bit.
I'd like to see more license classes than "Car, Car with Motorcycle rider, CDL (over 13 tons), and CDL with Trailer". One could start with a "light weight class" like moped/motorcycle/small car, then have a progressive system for "heavy weight cars" (SUV or pickup truck) or "high HP/Ton cars" (Sports car). These "advanced licenses" would have a higher standard of testing and stiffer penalties if you are driving a car that meets these higher-spec classes.
In Europe I've gotten tickets driving only 5mph over the limit (58 km/h on a 50 road), which would explain why the 85th percentile is closer to the actual speedlimit there.
I will admit though, she counsels me against following the rule in Virginia because the cops there don't mess around.
EDIT: I should add that 15mph over the limit is usually "going with the flow". If the other cars are traveling at 70 then 85 really stands out.
My usual rule is 5MPH over. I sometimes increase it to 10MPH, but it works almost everywhere.
If you are less than 10% over, the cops would need to prove that you knew it. This would involve testing your car. Nobody wants to bother with that, so you normally get an extra 10%.
Why? It would add time to your (and everyone else's) commute, while simultaneously being unlikely to substantially improve traffic safety.
It could be argued that the vehicle owner is responsible for ensuring this adjustment is made every time tires are changed, but with no real way for the average consumer to verify or measure the difference, the fact is we depend on the business providing the service to do it for us.
Plug an OBDII reader + app into your car to see the true velocity.
It's kind of funny to watch on the last two or three days of the month how many of the state troopers are out on the interstate, doing speed traps all day long. The rest of the month, you'll almost never see them, unless they are escorting an oversize load.
Just like the recent discussion about "troublemakers", 90% to 95% of drivers are - with different levels of driving competence - OK.
It is the remainining 5%, maybe 10%, that create most of the issues, directly or indirectly, that is not only speeding, it is often distraction, aggressivity at the wheel, etc..
One of the reasons why "black boxes" that record driving habits are not as common as they could or should be, besides of course the usual privacy risks, is that everyone is afraid if the data that would come out of them.
If all drivers were monitored it would likely come out that a small minority (the said 5% or so) should simply be deprived of the right to drive any vehicle (no insurance would ever cover them, as insurance is about risks, not about certainties) and this would break quite a few "social contracts", including the unwritten one in which there is a "right to drive" (because our cities and lives are organized in such a way that a car is needed to commute, to take kids to school, etc.).
This paragraph is really key. You want to design the road and the area around it to encourage an appropriate speed, and then set the speed limit at that speed (which should work out to the 85th percentile of what people would drive anyway). IMO most freeways, at least where I'm from, should have higher speed limits (and are already designed to support them). Some residential streets should probably have lower ones, but would need design changes to encourage people to actually drive at an appropriate speed.
Either they need to raise the limit or enforce it. I'm sick of being the asshole going too slow.
Also my speed is generally more a function of gas mileage than anything else. With stop lights littering the route I don't feel that driving 55 is any faster than 40. It just wastes more gas. So maybe it wouldn't even make sense to raise it and instead it just needs to be enforced.
In fact, I think it needs to go a step further - ALWAYS stay to the right. Only move to the other lane to pass or turn left.
No thanks!
Generally its the middle lane I use, but sometimes it's even the left if some landscaping truck or cement mixed is in front of me dropping who knows what into the road.
The randomness of having a human officer grab me (not the other 1,000 people) off the road for going too fast feels unfair and ineffective.
There are stretches in DC with exactly that strategy. As a consequence, people speed and then hit the brakes right before the cameras.
I'd love to know the accident stats right around those stretches.
[1] https://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pu...
You need to fix the core speed limit problem before fully enforcing the limits.
It's a fun (and annoying) game to observe how people's speed varies compared to the limit. I almost always go at the limit plus 5MPH unless that would make me dangerously slow. Sometimes this makes me the fastest car on the road, and other times the slowest.
There's a road I drive about twice a day where the first half has a 25MPH limit and the second half is 35MPH. I'm usually a slowpoke on the first half, building up a queue of cars behind me, and then end up the fastest car around on the second half. (And to preempt any haters, the 25MPH segment is less than a mile long, so I'm not severely inconveniencing people.)
Rural interstates here have a 70MPH limit, so I go 75MPH. Most people go 65-70MPH. As you get into the city where I live, the limit drops progressively to 55MPH, and most people go... 65-70MPH.
I really hope this is not the case
Some cops claim that aggressive traffic enforcement leads to knock-on effects in reducing gun crime:
https://www.nhtsa.gov/staticfiles/nti/pdf/809689.pdf
> Gun seizures by police in the target area increased by more than 65 percent, while gun crimes declined in the target area by 49 percent
It probably makes sense -- any kind of warrantless search has the potential to decrease crime.
I refuse to speed; I think it is immoral. This is because I ride a bicycle everywhere, and the extent to which people speed on surface streets has an obvious and tangible effect on my safety. My town has a narrow bridge that used to be the only way for cyclists to get across the river, where drivers routinely exceed the 35 mph speed limit by 20 mph or more. It is terrifying, and people have gotten killed. I wish they would put a speed camera on that bridge.
The argument that "the speed limit doesn't matter because people will travel the same speed" only makes sense under the assumption that the only people who will use the public roads are drivers who feel like they can do whatever they want. Plenty of drivers feel entitled to run red lights, too, and that causes more collisions.
Your situation sounds ripe for change. Look into street calming demonstrations, and seek neighborhood support to do one as well as possibly painting lines to narrow the lanes for drivers.
Just don't be surprised that drivers try to drive highways like highways, even when you try with signs to tell them that it's a low speed road.
But when driving on a limited access highway,I will speed most of the time because the speed limit is based on a now defunct national motor vehicle maximum speed law that was repealed over 20 years ago instead of an actual traffic and engineering study.
I would really like to see some consistency applied to how the law is enforced and written when it comes to traffic safety. What I mean by that is driving is clearly an inherently dangerous activity given the frequency of traffic incidents on a per-capita basis compared with just about anything else. Well, for every other type of inherently dangerous activity we are all forced to sign wavers basically saying that we understand and accept said risk and we are willing to take that risk. That acceptance protects mostly everything but situations involving negligence or gross negligence. I never understood why driving is treated any differently.
Also, when you look at what traffic law is at its most basic level, it makes little sense when compared to the rest of the body of law that exists for everything else. Traffic law exists primarily to increase safety on the roads and reduce the risk of accidents. Now, statistics do show that enforcing traffic laws do actually make the roads safer. I acknowledge that up front. But my issue with them is that the overwhelming majority of traffic citations are issued for violations that have caused no harm. That is, drivers are cited and forced to pay a fine simply for increasing the odds of an accident happening. The accident need not actually have occurred. Nowhere else does that shit fly. You can't go to court and sue someone for anything without there being some sort of harm/tort/injury/etc. That's basic law. If someone, for example, tried to defraud you but you were slick enough to spot it and stopped it, you can't sue them in court because you didn't actually lose money.
I'd much rather see a situation where either people accept the risks of the road and only have limited options like negligence and perhaps a few others - or, to see cops citing people only when they are deemed the cause of the accident or the rare cases when someone is driving so insanely on the road that their driving alone is enough to justify gross negligence (i.e. racing or doing 50 in a 25 in the rain).
Well, I might believe that if they didn't derive a sizable chunk of revenue from this enforcement. I think society as a whole might actually believe them if and only if it became a legal requirement that any and all revenues coming directly from fines are required to be donated to charity. Then I would be far, far more likely to actually believe that I'm getting a citation because the officer truly thinks I did something unsafe and worthy of being fined for. Since courts typically also assign a court fee if you decide to (or are required to) show up in court, there would need to be some kind of protection to prevent them from jacking up the court costs as well.
I don't know about the US, but in Germany there are many cases where you can be fined for decreasing safety, even if no accidents happened.
For example obstruction of escape ways, violations of fire safety rules, organizing large events without the required quota of paramedics present and so on.
Another category is the possession of weapons without permit, which is illegal even if you haven't shot anybody.
That wand exists - it's called "enforce the law". Increase penalties, or decrease them if you need a revenue-neutral plan, but enforce that 60MPH is a limit, not a suggestion.
This article parrots the same concept as most speeding solutions: speed doesn't kill, only variance in speed is dangerous. That makes perfect sense. So why increase the possible variance from zero, and why let people complain about driving at the limit being too slow? If you're above the limit, _you_ are increasing the variance, and _you_ need to slow down.
Enforcing the limits when they are artificially low helps no one except for the police.
Fortunately the cops in CA don't share your opinion.
There is very little benefit to increasing speed limits beyond the 85th percentile. The capacity of the roadway does not increase because of the increased headway between vehicles. As vehicles speed up, the distance between vehicles increases and thus the total number of vehicles that can occupy a given segment of roadway is decreased. At 30 mph, about 36 vehicles can fit within a one mile stretch (assuming 3 second following distance, 15 ft long vehicles and one travel lane). Under the same assumptions only about 16 vehicles would fit in a one mile section at 70 mph. However, slow speeds everywhere is not reasonable and that is why some measure of central tendency is used to establish speed limits.
Doesn't the upper limit of that usually match the 85th percentile speed of traffic?
> There is very little benefit to increasing speed limits beyond the 85th percentile.
Assuming traffic speeds follow a normal distribution, even those who exceed the 85th percentile speed don't exceed it by much (more than 5 mph). Beyond that, we're talking about 97th percentile speed or greater.
> As vehicles speed up, the distance between vehicles increases and thus the total number of vehicles that can occupy a given segment of roadway is decreased. At 30 mph, about 36 vehicles can fit within a one mile stretch (assuming 3 second following distance, 15 ft long vehicles and one travel lane). Under the same assumptions only about 16 vehicles would fit in a one mile section at 70 mph.
As traffic volume increases, the overall flow speed decreases which should offset the issues you noted.
Here in Switzerland (and throughout Europe), most limits are mostly sane. We have 120 km/h (75 mph) global highway limit, which you mostly don't want to ignore (especially in the mountains, which is like almost anywhere). And on the smaller roads, if it suddenly says e.g. 80 km/h, you better reduce your speed, otherwise you'll risk not fitting into the turn.
> 85% of drivers drive at or below the speed limit. ... > “I’ve found that about 10% of drivers truly identify the speed limit sign and drive at or near that limit,” says Megge. Since these are the slowest share of drivers, they don’t affect the 85th percentile speed.
If 85% of drivers drive at or below the speed limit, then why are the 10% who follow the speed limit amongst the slowest of drivers?
So the standard for acceptability is that you only see a crash (i.e. a tragic event, often with fatalities) every several months?
According to https://www.cdc.gov/vitalsigns/motor-vehicle-safety/ "more than 32,000 people are killed and 2 million are injured each year from motor vehicle crashes. In 2013, the US crash death rate was more than twice the average of other high-income countries." With that data, I don't know how a post that starts by saying this even gets this high in HN.
Car travel is more than one order of magnitude more unsafe than train travel, and two orders of magnitude more unsafe than plane travel. I think our grandchildren will wonder how people in our time were so crazy to drive around so much in cars, just as we now wonder how they were so crazy some decades ago to watch nuclear tests live or hold asbestos shoving competitions.
As for the argument of the overwhelming majority of people not obeying limits, I don't know the laws in the US but I suspect it may be relating to not fining enough. It used to be the same way in Spain until they introduced more fines the possibility of taking "points" off your license, which you lose for six months (and it's cumbersome to get back) if you get to zero. Now most people follow the limit or only drive slightly over it (there is a certain tolerance level below which there are no fines) and when some years ago it went temporarily from 120 to 110 km/h in highways, it was very visible how most people were indeed driving slower.
In Denmark we raised the highway limit from 110kmh to 130kmh on half of all highway. In the 2 years before and the 2 years after (ignoring the initial 2 months) the number of accidents and injuries on all roads fell roughly -15%. But on the highways with the new limit, it increased with 14%, and the average speed barely changed. The parts of the road where the 110kmh limit is saw significantly less accidents as well, probably because the average speed here decreased.
But the conclusion is fairly straight forward. The average speed barely increased, but the number of accidents rose significantly.
[0] http://www.vejdirektoratet.dk/DA/viden_og_data/publikationer...
There are fundamental differences in the way people in different countries approach driving and nothing's going to change that.
Swiss and Germans LIKE FOLLOWING RULES. It makes them happy (source: I work with a lot of both and they will frequently make statements like "Rules exist for a reason. If everyone just followed them the world would be better for all." Yes, I jump straight to Hitler with my counterarguments)
Americans do not. To an extreme detriment to their own health and safety (see: Airbag regulations that assume Americans won't have their seat belt on - a basic prerequisite to driving for literally everyone else on the planet. See also: socialized healthcare being "controversial").
Directly on either side of the toll road are the free roads. The only difference is one fewer lane each way. The speed limit is 60mph.
I do not believe there is enough difference between the two roads to justify a 25mph speed limit difference, except to create an artificial police-enforced incentive to fork over if you want to be able to drive as fast as you should.
I suspect many speed limits are designed in this way: either mostly arbitrary or calculated to maximize revenue (for police, toll road operators, etc.). They are not designed with optimizing driver utility in mind.
There are few things better than when you end up driving in a swarm of experienced drivers who are willing to safely exceed the speed limit. Safety (and efficiency!) in numbers.
The waste of space and resources that was required to put those extra lanes in, and all of the traffic control measures could have EASILY doubled the number of lanes on the beltway - alleviating traffic for many many years to come.
Instead, they've just created a false economy around the pricing of convenience. It's essentially rent seeking by the government.
I still find myself speeding up to match the flow when the roads are busy though.
Can you be prosecuted for driving at the speed limit in the fast lane? It seems like nobody would be legally allowed to use that lane if that were the case.
John Nestor tested the law in D.C. He was the major force in bringing to light the effects of Thalidomide in the early 1960s. He stood up to drug companies.
> A plot was hatched, fueled by indignation: "By God, I've paid taxes for a long time -- and more than a lot of those trucks." First he consulted with the commonwealth attorney's office and other traffic authorities to ensure that his plan was legal, that passing on the right was acceptable on multilane highways and that traveling over 55, even to pass, was against the law.
https://www.washingtonpost.com/archive/lifestyle/1984/11/21/...
One of the reasons they would prefer to flush you out of the lane rather than pull you over and give you a ticket is that the very action of pulling you over (possibly across all lanes of traffic) and sitting on the side of the road while ticketing you causes other drivers to slow down (sometimes erratically) and increases the likelihood of a collision.
The CalTrans manual for setting speed limits includes some references for many of the issues this article is discussing: http://www.dot.ca.gov/trafficops/camutcd/docs/california-man...
https://www.motorists.org/press/montana-no-speed-limit-safet...
I also believe it came out that the company providing the cameras was getting a cut of every ticket issued, leading to a tendency towards false positives. The program wasn't profitable for the state and people complained so much that the cameras were gone a short time later. I remember most people would slam on the brakes just before the stationary cameras, cruise through at exactly 64 or 74 mph (the cameras went off at 10 mph above the posted limit) and then accelerate to whatever speed they wanted. It was way worse than people just speeding.
Maybe it works well in S. Korea because the incentives aren't so screwed up, but here in the States "Cameras" mean someone is getting a cut and the people are getting screwed. The camera's get set up in the best places to get revenue (downhill when the speed limit changes from 65 mph to 55 mph around a bend so you don't even see the sign before it's too late).
Pretty much no-one seems to obey the official speed limits, instead opting to go with the subjective "safe speed" as per the current weather conditions, traffic flow, visibility etc (just like the article explains).
Is your experience driving in S. Korea that different?
That said, in addition to safety, cars get lower gas mileage at higher speed (above about 50 mPH). Every time I see someone speed, follow too closely, or is careless in lane changing, I think "there goes a selfish a$$hole who doesn't care about the safety of others or the environment." I have never had a speeding ticket, BTW. People who speed and drive carelessly are self centered a$$holes.
.... although the yellow stripe between opposite directions of traffic is something the rest of the world sorely needs.
"The United States' only contribution to the modern world" to paraphrase Jeremy Clarkson.
People focus on whether the speed limit will be respected and not on what the full consequences up.
(Right now I can find a couple studies, but they're mostly from... insurance lobbyists? I feel like the interests are aligned there but lobbyists so...)
The intuitive explanation is to consider that every instance of passing or being passed is an opportunity for a collision, and increasing the number of instances (either by being faster and passing many vehicles, or by being slower and being passed by many vehicles) will inevitably catch up to you the longer you do it.
Meanwhile, there is a lot of well-done research around this. But several factors get in the way of doing the ideal thing (which is usually to put the speed limit either at the design speed of the road segment, or at the 85th percentile of observed traffic speed). The biggest problem is political forces causing a road to have a posted limit significantly lower than its design speed; many people will, unless they're laser-focused on the speedometer, end up driving around the design speed of the road regardless of posted limit, because they'll take their cues from the road (width, length of curves, length of turning and merging lanes, etc.) rather than from infrequently-placed signs.
Germany: 4.3 deaths/100k inhabitants, 6.8 deaths/100k vehicles.
United States: 10.6 deaths/100k inhabitants, 12.9 deaths/100k vehicles.
Germany: 4.9 US: 7.1
I'd say that's a more reasonable measure.
I had this wonderful experience in the south of Portugal, where they had traffic lights that would only go on red if you were speeding, and if you would ignore the red light you would get a fine for it.
I thought it was pretty genius.
Instead, many people seem content to do a bad job modulating their speed with the pedal on hills, and average just under the speed limit instead; or swerve like a maniac across as many lanes as it takes to get ahead a few car lengths. It's really frustrating.
That's the behavior of my wife's cruise control on her truck; we have to set it to account for 8-10mph slop on either side of the set point, depending on the slope of the hill. It's not even an old truck...
That's why it's so bloody dangerous that clueless folks plod along in the left lane obstructing traffic. It's extremely common to see 1/4mi or more of open roadway ahead of knotted up traffic driving the same speed.
The ticket is only a small part of the actual costs.
And even worse, while this combination-punch can be irritating to middle- and upper-class folks, it can be financially devastating to someone living on the edge of sustainability.
But then, somebody has to pay for all those shiny new Police Intercept cruisers, SUVs, tactical body armor, new weapons & training, drones, robots, etc. etc. etc.
The article implicitly accepts the conventional 85h percentile rule as defining correctness, and it's the single most common rule used to set speed limits in the US. Yes, some are below because of rounding rules, and some are below because of special safety conditions (in California, in general, these allow 5mph downward departures), because of specific legislative exceptions (school zones), or because of state maximums (which mostly affect major highways, not city streets).
And, outside of restricted-access highways, while the 85th percentile rule may be ideal for automotive traffic alone, there's a reasonable case that it's too high for mixed uses. [0]
[0] An example of the argument is here: http://la.streetsblog.org/2016/06/15/legal-obstacles-to-safe...
I used to drive 62 miles round trip to work, worked at home for a bit in between and am now back to about a 30 mile round-trip commute. Both were split equally on surface and freeway roads. Back when the speed limits were lower it was generally expected that most drivers -- during rush hour (assuming one could reach the speeds) -- would drive 50 MPH in a 40 and around 55 in a 50. It always surprised me -- every morning and evening on about a 6-mile stretch of road marked 40 MPH, there wasn't a car driving under 50 (and when that rare driver arrived, he was often tailgated so hard that traffic safety decreased considerably for him). Then, out of the blue, almost every road I took to work was changed to 50 MPH. Surprisingly, people weren't suddenly driving 60 MPH. I'm now on a similar commute as I was years ago, taking that same road, and people are consistently driving between 50 and 55 MPH on it.
I love our 85th percentile rule. It makes sense -- that one driver who's obeying the speed limit is being tail-gated by everyone else, reducing the distance between him and other cars, which increases accident probability and the relative severity of the accident since it will happen at a higher speed due to reduced braking time. When everyone is going about the same speed on the road, cars tend to be more spaced out and the relative difference in speed between the two objects colliding affects the severity of the accident.
There's also a lot of misconceptions about how speed is enforced -- at least in my area -- and what rules exist around speeding. I'm not sure if this is still the case, but it used to be that you were legally allowed to exceed the speed limit by 10 MPH on a freeway to overtake a vehicle in the passing lane. I have family who work in traffic patrol for the county and this topic comes up regularly. The department they work in encourages targeting people driving in excess of the speed of traffic, not folks who are keeping up with the speed of the cars around them. Of course, you can be pulled over in this scenario, and you are breaking the law[0], but at least in my area, it's not encouraged. An orderly system is safe, an outlier is unsafe, so they aim for folks who are driving in the left lane on a freeway in low traffic volumes, folks going over 20% of the speed of others and exceeding the speed limit, people jumping solid lines[1] and the huge problem caused by large numbers of people running red lights and failing to yield right-of-way when turning left[2].
[0] Both of them will tell you "If I want to pull you over, I can find a reason". A common one is those plastic covers/dealer advertisements around license plates or things hanging from a rear-view mirror. Some of the plate variations are legal (but there are very specific rules and almost all of them are not -- it's just rarely enforced), but most things hanging from the rear view mirror are obstructions.
[1] There are many places on the freeways in Michigan where the lane markers are solid white and for some reason, people don't understand that it's illegal to change lanes -- that's why they're solid. Aside from safety (they're put in due to increased blind-spots that make lane changes unsafe), they're often located in areas where people are entering the freeway and backups occur. Folks who panic at merging traffic or just don't want to slow down will jump lanes ... causing a worse backup.
[2] I realized this is going to sound uncommon to folks who don't live here, so pardon the long explanation. Easily the most common issue on road-ways in my area is people failing to yield when turning left at an intersection (my cousin/uncle will tell you this, but if you live here you're either already aware of the problem, or you aren't realizing you're doing it). Red light running is also more common here than in most of the country because of the frequency with which people encounter one-way intersections. It's legal, everywhere (except NYC and a probably a few other corner cases), to turn left on red when the road is one-way. Where I live, every road over three lanes (and many under) are engineered using the "Michigan Left" (https://en.wikipedia.org/wiki/Michigan_left). Often, though becoming less common, the "turnaround" is configured so that you can only turn left onto the same road heading in the opposite direction. Everything's fine when this is the case. However, it's grown popular to position these turnaround lanes in places that coincide with large retail business entrances or moderate traffic side-roads. All bets are off here. Because people are used to turning left on red in these turn-arounds, they assume they can also, legally, go straight into the side-road/business on red. Go ahead and google for signs telling people not to run red lights ... I couldn't find any. We have several of them on Hall Road in Macomb County. People are also used to "just going" when it's green, but you can't do that if the turnaround has traffic entering the road on the other side -- all of that traffic is turning right and has the right-of-way, just like in any other intersection -- left must yield unless they have a green arrow. I've been honked at on more than a few occasions by other drivers for not just plowing into the intersection, or not running the red to enter a side-street when traffic is clear but the light is red. Worse, once they put these hybrid side-street/turnarounds in, it destroys any advantage that the Michigan Left supposedly provides. It's already at a disadvantage since a portion of the traffic now has to pass through an intersection twice, but now the advantage of the "increased flow due to reduced traffic light phases" is overcome by the backups occurring in both turnarounds bleeding into a lane of traffic and the sudden pouring in of new traffic -- which has priority over existing traffic due to right-of-way -- entering in from popular businesses and busier side-streets (and, yes, a vein is popping out in my forehead now).
Do any/many states have lower ages?
Not seeing a person dying in an accident in the last couple of months is not a good enough excuse for me. Even the fact that I know 1 person in my life who died in a car accident means that we should be stricter in law enforcement with speed limits.
What we need is autonomous vehicles, because the sad truth is that a very large portion of the driving population should never have been issued a license in the first place.
Don't even get me started on the 85th percentile thing. That is a poster child for lazy engineering and government.
Do you have a citation for the increase being caused by inattentive drivers? There could be other factors, such as more people driving instead of flying, for instance.
But I do wish everyone would just drive to their abilities rather than some prescribed upper limit. Our laws made sense back when you still found carriages on the road. (Sorry Amish).