In Canada, its kph, but theres a sign when entering Ontario from Manitoba, where the speed limit is 90 kph, “fines starting at 100 kph” and it lists how much the fine is for doing 100, how much for 110. So the Ontario gov basically sanctions doing 99 in the 90 zone, just dont do 100.

Meanwhile Ireland:

Speed limits are designed for suboptimal road conditions. Since dynamic speed limits weren’t even possible until relatively recently, they figured out how quick you could safely travel on a road when it is nice, and again when it’s crappy, and set it somewhere between those values.

3. Why is traffic enforcement given to very expensive and ineffective police instead of cheaper and more automated traffic cameras?

Fuck. Off. With. Your. Surveillance. State. Bullshit.

85th Percentile Rule (where applicable): In many states, a common engineering principle is to set the speed limit near the speed at which the majority of drivers travel under free-flow conditions. Some states adapt or supplement this approach with safety-oriented judgments.

https://thelegalguide.org/who-decides-speed-limits-federal-state-local-roads/

I think the dissonance about speed limits is why there are so many awful drivers, at least in my neck of the woods. You go through drivers ed and you’re trained to go exactly the speed limit in all circumstances, and then you get let loose and find out on some highways, driving under the speed limit is so slow compared to the actual rate of traffic that doing so would be dangerous. People learn that and figure that all of the rules of the road are stupid and bad and you have a country of awful drivers

it doesn’t help that, as another commenter mentioned, you can be ticketed for not moving with the flow of traffic. follow the law, and you’re still breaking the law! plus all the asshole drivers who will get right up on your rear bumper if they decide you aren’t going fast enough. damned if you do, damned if you don’t! although ultimately, going slower is almost always the better choice from a safety standpoint because of that whole “physics” thing

And, yes, I know there’s some thing people did long ago to set the speed limit at some percentile of what people were already traveling at, but that’s obviously a stupid way to do it and we did it anyway. So why?

I’m going to disagree about that being a stupid way to do it, for two reasons.

First, there was a time traffic engineering was not a well-developed field. There was no expert who could combine science and best practices to get a good answer about how fast it’s safe to drive on a particular road because humanity had not yet learned that skill. Measuring what most drivers do, then reducing it if people crash a lot in a particular place is far from the worst approach.

Second, it’s bad to make laws that most people will only obey with heavy enforcement. It’s bad for a society to make lawbreakers out of most of its members, and to create pretexts for police to stop people without other evidence of wrongdoing. If there’s a reason to make most people drive a particular road much slower than they actually do, any reduction in speed limit should also be accompanied by changes to the road design (traffic calming).

Genuine answers from what I’ve heard regarding laws at least in CA:

1. There is a precedent that you should be going with the flow of traffic, which is technically safer than going the speed limit when everyone else is faster-- but mostly only on freeways; I rarely the flow going that fast on streets, so the rule doesn’t apply to that one jackass going 60 in a 40 zone. And yes, you’ll just get to the red faster (good cities time popular traffic lights to the speed limit so it’s even stupider to speed).

2. I’m pretty sure they also set the limit to what older vehicles can pull off safely (assuming you don’t tailgate, anyway). They have upped the limit in some areas, however, which I found upsetting. Like, 70mph up from 55mph over a few decades, which feels fast.

3. Traffic cameras are used, but there’s an interesting issue on legality. If you don’t acknowledge them, they can’t actually say you got the ticket (they come in the mail). I forget the details, but something about seeing your accuser? LA itself more or less decriminalized them, but your mileage may vary based on local government.

4. Places do, in the form of speed bumps, stop signs and curved roads. Not using those is probably more a mix of old roads and poverty-- new suburbs use windy, wide roads. Wealthy neighborhoods install speed bumps and add tons of stop signs. I don’t see it in my neighborhood because “it’ll hurt business” which feels like code for “you don’t matter enough for safety,” hence I think it’s a wealth inequality issue like most things in this country.

Anyway, that’s the best of my knowledge as a CA resident. Honestly, the bigger danger to me are people who tailgate, road rage, drive on sidewalks, and do stupid things to get to an offramp. That last one? Just last Wednesday I saw a guy, car totaled, who tried to hit an offramp they missed by sharp turning into it, going up a 55 degree slope, and getting t-boned by another guy going up the normal way.

Idiots, I swear…

Wealth inequality is so outrageous. I sometimes have to cross a 4 lane road to get to an official bus stop. I mean, they built a fucking bus stop, and the fucking bus stops there multiple times a day, they have to assume people are crossing the street at least once. Signage? None. If I get hit, it’s my fault. I sometimes have to wait a few minutes at rush hour for a safe time, and thank god there’s a generous median or I’d be just standing in traffic doing hailmary’s just to get home.

But I live right near a lake and when those rich fucks want to cross the lakeside road to go from their mansions to their private beach there is a fuckton of signage:

WARNING: CROSSWALK AHEAD

SLOW

CROSSWALK AHEAD

STOP SIGN

BLINKING RED LIGHT

CROSSWALK

And that’s when they actually WALK to the beach because most of the time they’re taking their little private golf carts.

I understand why the French Revolution went the way it did.

1. Go fast

2. Go faster

3. Allows for invasive searching that cannot be performed by a static object

4. Go fast but circle means slow

Thanks for attending my TED Talk.

A lot to unpack here. Many reasons for all. Since I’m typing with my thumbs, and this will be a long one, I’ll be glossing over some details.

Why does everyone drive 10-15 miles above the speed limit?

There are many reasons, but the two biggest are:

1. The systemic issue road design often not reflecting the safe speed of that road.
2. The systemic issue of traffic enforcement also being a means of fundraising for police, thus making only the “big” tickets worth their time.

Why don’t we raise the speed limit if that’s how fast everyone wants to go?

The better option is to design roads such that a lower speed feels more appropriate to the given conditions.

Why is traffic enforcement given to very expensive and ineffective police

The systemic issue of US police being trained to believe they’re warriors in battle, thus many of them seeing traffic enforcement as not worth their time. The better question is, why are law enforcement and traffic enforcement carried out by the same people?

instead of cheaper and more automated traffic cameras?

The US Constitution guarantees the accused the right to face and question their accuser in a court of law. Rules of court procedure guarantee a witness cannot offer evidence to an event they didn’t personally witness. This makes prosecution via camera problematic; the camera can’t be called into court for questioning and no person personally witnessed the event occur.

Why do we refuse to ever use ANY traffic calming measures? Yes, than you flashing digital sign for telling me I’m going 10 miles above the limit on this incredibly wide and straight and flat road with high curbs and perfect visibility.

The systemic issue of widespread corruption, resulting in projects being completed as cheaply as possible, as opposed to as effectively as possible. Proper measures requires hiring engineers to determine what’s needed and then installing them. Every dollar spent on that is a dollar their friend who was contracted for the project can’t pocket and donate during their next campaign.

US Americans aren’t stupid. Their government has been captured by corrupt officials and oligarchs who are making money off the status quo.

1. Because the ratio of drivers to law enforcement allows it.
2. How speed limits are decided is very complicated. What people “want” isn’t the top priority.
3. Because automated cameras are owned by profit-seeking entities with zero incentive to handle this data appropriately. See: recent Flock abuses as examples.
4. Those exist but, once again, the ratio of signage to driver is poor.

Most of your questions also are rooted in what appears to be a lack of appreciation for just how huge the USA is. We can’t possibly police all of it and there are very, very good reasons why we shouldn’t even try. Especially with the current demented leadership.

It’s because the speed limit is set to the lowest common denominator. Same way a fleet of ships can only go fast as the slowest ship. Most people can drive faster safely.

It’s also to make sure the law can always find sonething to use against you when they decide you need to be punished for standing up for yourself.

I find it frustrating that in the US at least, people can’t do the simple math. Unless it’s a very long trip, speeding doesn’t save you very much time at all. A couple of minutes at the most for a typical commute.

On countless occasions I’ve seen some some reckless moron nearly take other vehicles’ bumpers off to ‘get around’ traffic. And then you’re right behind that same moron at the next red light.

They are risking everything for little to no time savings.

Ignoring largely empty stretches or highways where there’s practically no signs, have you seen how many signs are out there on heavily occupied highways?

We’re just coming out of Gulfport Mississippi, Highway 49 (don’t worry I’m riding passenger, not driving), and it’s pure information overload. When you’re surrounded by like 500 signs, McDonald’s, Circle K, RaceTrac, Shell, Chevron, this and that doctor’s office, etc, and you’re only looking for the BIG signs to see what exit to take, well its all too easy to miss the random speed limit sign that they don’t even post but once every 3 miles or so.

When surrounded by signage information overload, while you’re supposed to be keeping your eyes on the road, you simply cannot read every damn sign. You mostly keep your eyes on the road and follow whatever the pace of traffic is, only glancing up and around for the green signs with road names and highway/interstate directions.

The rule of thumb I’ve learned, is that no matter the posted speed limit, as long as you’re driving safely about the pace of traffic, and aren’t the idiot darting through 20mph faster than everyone else, then the cops generally aren’t gonna mess with you.

School zones are definitely an exception, you better be going 15mph along with everyone else, and of course following the directions of the traffic guards and bus stop signals when to stop.

TL;DR - Too much information, cannot read all signs and keep eyes on the road simultaneously.