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Comment by josephcsible | Hacker News Reader

This is evidence that most speed limits are too low. The proper speed limit on any given road is the 85th percentile of what drivers actually do.

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No, the proper speed limit is one that is decided based on traffic engineering safety factors such as sight distances, and who else uses that road.

Cities aren't dropping their speed limits to 25 mph for shits and giggles. They're doing it because the odds of a person on foot or bike surviving being hit by a car goes up dramatically when speed drops from 30 to 25. Fatalities drop to nearly zero at 20mph, which is why many dense residential side-streets are 20mph. It also has the nice side effect of discouraging people Waze-slaloming their way through neighborhoods instead of using major routes.

https://nacto.org/publication/city-limits/the-need/designed-...

The whole "make the speed limit what most people are doing" was just auto industry bullshit that helped make our roads even more dangerous to people not in a car or truck.

> It also has the nice side effect of discouraging people Waze-slaloming their way through neighborhoods instead of using major routes.

I wish cities would solve this problem by making the main roads faster instead of by making the side streets slower.

You aren't solve the problem of "Too many people are driving on the arterials, so traffic is going too slow" by making driving faster and more attractive.

> The whole "make the speed limit what most people are doing" was just auto industry bullshit that helped make our roads even more dangerous to people not in a car or truck.

Hard disagree. It is simply an observation of reality, and a very useful reminder to anyone who wants to waste time and resources putting different numbers on signs. You have to actually engineer the roads for the speeds you want, and I get that it's more expensive than just painting new signs and telling your constituents how much you're trying to help.

We have neighborhoods where cars cannot pass without one giving way and pulling off into the parking area. Is it inconvenient? Sure, sometimes, very much so. But you know what? People drive damn slow. Nobody cuts through the neighborhood to save time when traffic on the arterial road is congested. It matters not one bit what the speed limit signs say (there aren't any, actually), because road design solved the problem neatly.

If the speed limit that was deemed safe for an area is lower than the 85th percentile driver speed, then that road is poorly designed. It should instead be redesigned such that people slow down themselves, regardless of what the sign says.

Speed limits in California are capped at 65 mph by state law (or 55 mph for undivided roads). Any agency wanting to set a lower speed limit has to conduct a speed study and cannot set the limit lower than the 85th percentile of measured traffic speeds.

Of course they can skip the speed study, or not repeat it every 5 years as required, but then tickets are effectively unenforceable on that road.

They can also increase the speed limit:

> Department of Transportation, with the approval of the Department of the California Highway Patrol, may declare a higher maximum speed of 70 miles per hour

https://leginfo.legislature.ca.gov/faces/codes_displaySectio....

While most roads are indeed capped at 65, stretches of I-5 are set to 70 , there is a process for this I believe.

Highways like the 101 are 55mph in some parts. Whats most dangerous about californian freeways are the people with ten feet of metal scrap in the truck bed going 40mph in the middle lane.

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