Cops won't pull you over or write tickets if you're not at least 15 mph over, we basically don't have speed cameras, everyone's trying to win the rat race and dehumanizing other cars around them, and it's not considered morally wrong (by most) to break that specific part of the law.
So a single vehicle obeying the law will quickly get a long line of tailgaters and tailgaters of tailgaters trying to "push" the vehicle to go faster.
They can suck it, I'm not late or in a hurry, and my ancient truck, steel bumper, and class 5 receiver hitch will not be badly harmed by your plastic grille. I get better gas mileage and have a longer stopping distance when I drive the limit, and I don't care if others are honking or riding my ass because they think I should drive faster.
I've been rear-ended in my truck, and the receiver punched a nice hole right through the radiator of the guy who hit me. Definitely fucked his car up way more than it did my truck ... except man, that is definitely one of the hardest impacts I've ever felt in my body. I now appreciate how hard the head rests really are, despite looking a little soft. I think I'd rather have crumpled crumple zones and a new truck next time.
A lot of science and work goes into the construction of those headrests - if it was less firm, you'd get a concussion from the rotational forces in the whiplash or just break your neck, more firm and you'll get a concussion from the linear impact. It's not at all arbitrary, there's a reason they are exactly as firm as they are.
The speed limit itself is a separate convention and regulation. In some places you can be cited for obstructing traffic by going the speed limit in the passing lane if you are matching the speed of cars to your right, effectively blocking the road.
It's not just customary in many (most?) states, it's the law. People who sit in the left lane are the problem.
The last couple laws like that I checked only talked about limiting flow below the speed limit.
A custom that (where I live) is becoming more honored in the breach than the observance. It makes driving very much more dangerous.
In Britain they have a sardonic nickname for people who do this: CLARAs. "Centre Lane Residency Association".
I think this undersells it a little. It does not just impede faster traffic, when the lanes are pacing each other it makes navigating harder -- simply switching lanes is more difficult. The highway moves so much more efficiently with a small but steady difference in speed between each lane.
"Only 46.5 percent of U.S. drivers consider going more than 15 miles per hour over the speed limit on the freeway to be "extremely" or "very" dangerous — with 40.6 percent openly admitting to doing it at least "a few times" in the last 30 days" [1].
[1] https://usa.streetsblog.org/2023/11/30/why-so-many-u-s-drive...
Most Americans ignore speed limits. This stems from it being socially and legally problematic to permanently revoke our driver’s licenses. We should raise a lot of limits. But many others are fine and still sped through.
But there are also people who drive in the left lane, who will tailgate you at 1 or 2 meters because you're doing 130 km/h. These people are idiots, but you get these sorts of people everywhere.
On American freeways, you don't have a choice, every lane is doing about 10 mph over the limit (or in LA way under) and it is disruptive or dangerous not to. These freeways tend to be running at full capacity so it actually makes sense since it improves capacity.
In theory, braking distance scales quadratically with speed. In practice, people leave less room on highways, because they rely on others driving predictably, but spacing still increases faster than linear.
