This. My city keeps putting in more and more traffic cameras, but it doesn't slow cars down; it just generates revenue. If they actually wanted people to slow down, they'd reconsider having the main road look like a pin-straight four-lane highway.

Behavioral engineering is way more effective than posted speed limits that often didn't seem to correlate with reality.

If you give me a five lane stroad with wide lanes and lights only every 1/4-1/2 mile, I don't care what the speed limit is, I'm doing 60+ because it feels right, and if someone does the speed limit in front of me I'll probably be annoyed.

But if I was going down the same street, doing the same thing, with the same amount of time available, but the lanes were narrowed to add protected bike lanes, the center lane was replaced with a median with trees and occasional left turn/u-turn spots, and crosswalks were added between the lights, I'm going to do around 35 because that feels right, and I won't even be mad about it. I'll just cruise down the street chilling.

Give people a street where it seems like you should be going fast and people will go fast, and get aggressive/angry when they can't. Give people a nice street to roll down and chill and that's what they'll do. It looks nicer and is more walkable/rideable too.

Right, this is one of those things where I seemed to have a very different experience than many Americans …. But we have older roads that are narrow and winding. The towns were all built out before cars and never really got to the “stroad” stage of dystopia. All those “design elements” come for free

I mean, if you're on a bike or power walking or something I'm certain nobody's going to get too disagreeable about your speed.

“why was this neighbourhood road designed like a freeway”

The stroad by my house is five lanes wide with a 45mph speed limit but still has crosswalks that nobody can use because it's a five lane road with people doing 45mph and many people have already been killed crossing. So many that children are bussed from the school across the road because it's too dangerous to even have a crossing guard.

You read that right: Kids who live less than 200 feet from the school can't walk there because the road is too dangerous.

And we can't get the speed limit lowered because it's a state highway and the state says it has to be 45 and the local community has no say in it.

And people wonder why I hate authority.

from the size of lanes

Wide lines! luxurious!

As noted car enthusiast NotJustBikes has said, driving is not a conscious activity. We drive to what feels right, to a degree. A road built to support 100kph will always have speeder problems until layers of traffic calming are put in place.

UK B road limits are in fact limits (as opposed to North American suggested minimums), often being little more than millennia old cart paths with asphalt applied

If you look at the design documents for the roads in your area, usually available in plain old PDF files at your State DOT website... it usually states both the designed speed, and what the posted speed will be.

If it's a modern road, it is almost certainly designed for 5-10mph over what the posted limit will be. Because they know most traffic will speed, and that is accounted for in the road design, regardless of the posted limit sign.

When I was in Appalachia, on the mountain roads, many are very narrow, and winding. Speed limits often like 40, and you can't go more than that without crashing unless you have a motorcycle or something. It's not a suggestion, it's the maximum you can do on the curves.

You are right about American freeways. City roads tend to have a lower speed limit that is probably appropriate and it would be unsafe to go faster.

Rural America will have little roads with deer and intersections at blind curves and say 55 mph seems about right.

The other aspect is that we typically are against automated enforcement regardless of the law.

We typically want people to be in the loop. If there were more visible traffic cops, people tend to slow down to the limit.

Another factor that hasn't been mentioned yet is it gives cops pretty unilateral right to pull you over if they feel like it. IANAL, but in many places it's illegal for a cop to pull you over just for "being suspicious", but because of speeding and various other traffic laws on the books that are almost universally ignored, they can pull you over for speeding, then decide you seem suspicious and search your car, breathalyze you, etc.

Prima fascie.

No body is driving perfect, speedometers aren't perfect, and such automatic devices aren't perfect nor can they identify the driver yet. I believe they use these elsewhere like UK... But most likely have a bit of wiggle room

It may be necessary to speed up to avoid or pass something reasonably and ultimately the speed limit is so for most conditions. In a 70 it may be reasonable to do 80 on a clear, sunny day with minimal traffic. After all it's still 70 at dark when your visibility is cut way back. Plus it can't be a hard rule given weather conditions, traffic speed differentials, etc... 70 may be too fast or otherwise.

It's not that big of a deal unless you're the one driving too fast or slow relative the everyone else.

If that happened people would avoid toll roads which means there won't be enough toll income.

There's lots and lots of laws like that

Like perjury. It's almost never pursued, the judge will just order your testimony ignored

Or paying your taxes. You're basically expected to do your best to cheat, especially if you're a corporation

There are plenty of stories in our folklore of times people sped 100+ just to get to the emergency room on time.

Especially since it's not even criminal.

They don't do it because the U.S. has good standards for what is a crime.

For example cops can't tailgate you then give you a ticket for speeding.

Additionally, doing this only on freeways would probably make the roads less safe as drivers would go faster on surface streets. Thr 65mph speed limit was set in the 1950s by 1950s white men for 1950s cars. Freeways are safer than surface streets by multiple factors of 10.

That's not a bad strategy. Driving slowly on slow roads or in adverse conditions and fast on highways seems rational to me. What is the point of making a road that is specifically designed for high speed and then putting a limit on it? The speed limit is an incredibly blunt instrument for deterring bad driving, as if driving below the limit is always going to be the safest option. It also motivates law enforcement abuse. The vehicle-environment-driver complex is much more nuanced than a single variable threshold.

It's worse than that. If everyone speeds all the time, cops have a valid reason to pull over and harass anyone they choose, on the pretext of speeding. You'll never guess what demographic gets a disproportionate amount of police attention despite not speeding (or committing other traffic violations) significantly more than average.

It's pretty much codified. 9 mph over means pretty much nothing. If you are a little over that? Everyone knows the courts will probably knock it down to 9 over just by asking.

As another comment points out, it's works for being selectively enforced. Almost every car on the road can be pulled over. Even if you are going the speed limit, you might get pulled over for impeding traffic.

Just go the speed limit and keep in the travel lane, people can pass if they want to go faster than the speed limit.

Are there workers? If there are workers, slow the heck down, keep them safe. If there are workers, it shouldn’t even be a question

During the Arab Oil Embargo they lowered speed limits on highways to 50 mph, which is the most economical speed to drive.

Windows up is more efficient also, as is fully inflated tires.