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Comment by cardy31 | Hacker News Reader

Speed limits are 100% political. They aren’t based on engineering. You always have cops saying “speed was a factor in this collision” and “everyone just needs to slow down to be safe.” But the reality is that accidents don’t happen from high speed, they happen from a high standard deviation among speed of individual cars on the road. Having a speed limit well below what the road can safely be driven at creates that high standard deviation as some people drive to the road while others drive to the limit.

The collective insanity that we as a society have around setting sensible maximum speeds for roads is one of my bigggest pet peeves.

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> a high standard deviation among speed of individual cars on the road

so in a world without speed limits, people can individually decide what speed a road "feels like". in a world with speed limits, people can still do that but there's a sign stating a preferred speed for the road and an (admittedly flawed) enforcement mechanism.

I really can't fathom how the former leads to less "deviation" than the latter.

not agreeing with post you responded to, but you're misrepresenting them.

my understanding of the post is that he proposes speed limits should not be set so low as to increase the deviation between people following the speed limit and following their intuition i.e. they should approach average intuitive speed of the drivers using the road.

We do seem to end up with a ratchet effect though. My town sets speed limits at the 85th percentile of speeds based on traffic surveys. Say the limit starts at 30. Most drivers assume a buffer before there will be enforcement, so they start driving 35. Next time the city studies that road, they raise the limit to 35 and drivers start going 40. Rinse. repeat.

Eventually, you end up like our main road through town where the limit is 45, the state limit for that type of surface street. Many drivers are happy to go 50 but the area has built up and also gets a lot of drivers unfamiliar with the area and those drivers go 30. It's a real mess and there are multiple crashes daily but I don't think the speed limit will ever be lowered. I think I've only seen the speed limit lowered on one road in the almost 20 years I've lived here. They only change in one direction.

Leaving aside the simple physics of more kinetic energy making those 'standard deviations' clearly more serious for all involved, we clearly don't want high speed traffic in environments with pedestrians and cyclists. So while the Autobahn may not be a nonstop catastrophe, I would think it's clear that speed limits on non-freeways are far from "100% political".

>I would think it's clear that speed limits on non-freeways are far from "100% political".

This depends on the locale, and what you consider "political". For example, in NYC it is entirely "political/financial. For some time now the city-wide speed limit has been set at 25 mph, with thousands of speed cameras that automatically ticket people. While on some streets this may be reasonable, it is certainly not reasonable city-wide (which includes all the outer boroughs of Queens, Brooklyn, Staten Island and the Bronx). In her annual address this month, Governor Hochul announced that the city-wide speed limit will be lowered even further, below 25 mph! This means that at the maximum legal speed, your car will be passed by bikes, mopeds and even fast runners. This is clearly not a safety issue, thought some will argue it is "safer" (and it would be safer still if the speed limit was 0, nobody would ever die from an auto accident!). It a combination of a money-making scam and a political ploy to curry favor from the small (but politically powerful) group of New Yorkers who want to eliminate cars all together.

To be clear, a huge majority of crashes happen at the interface points between multiple traffic streams. Higher speeds in that situation is absolutely both an exacerbating factor in the likelihood of a crash (by increasing the stopping distance) and the severity of the crash when it happens.

The ticket is to design roads such that people naturally drive at safer speeds. The collective insanity is that we as a society allow engineers to pretend that features intended to speed up traffic are a safety mechanism.

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