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by bsder 3056 days ago
Ah, yet another Strong Towns anti-car screed of "let's make all roads so damn slow nobody can actually get anywhere" without any discussion of the downside of what they propose.

I've lived in "Cannah get theyah from heah" Boston. I can assure you that slow, safe, crappy, narrow, winding roads suck as bad as you think.

Or try going from Braddock to Penn Hills in Pittsburgh, PA. Nice and slow and infuriating. There's a reason why a whole bunch of people decided "You know, that nice empty area west of Pittsburgh with roads that actually let you get from A to B is very enticing."

> One can easily notice that most folks seem to treat the speed limit as a minimum speed rather than a maximum speed.

I disagree. People simply IGNORE the speed limit and drive at what they consider to be a safe speed.

Part of the problem is that there are political forces (cough police budgets) that encourage stupidly low speed limits. If all roads were set at the appropriate speed (something like 85% of traffic, IIRC, but there is an actual engineering number), suddenly "speeding" becomes an actual traffic safety issue.

And, in fact, ignoring a speed limit is a rational decision when everybody else would be going 10-20mph faster than you. Absolute speed means more damage when a accident occurs, but relative speed differentials mean more accidents occur.

2 comments

Didn't read? That 85% _mantra_ is mentioned. Yes, it's an engineering principle...designed for rural roads. Blindly applying that to all other road types is not engineering, that's cargo cult.
Can someone please explain the 85% thing to me? I've read both the comments and article and still don't fully understand what it is. Maybe I'm stupid.
Not 85%, but 85th percentile, apparently.

https://metrocount.com/downloads/flyers/Speed_analysis_1.pdf

I'm not a traffic engineer so I'd love an explanation, because on the first look, it seems absurd to apply this measure to determining speed limits, as a) 85th percentile will keep creeping up with each iteration of such speed limit adjustment, and b) the whole rationale seems to depend on "wisdom of the crowds", i.e. trusting greedy optimization to find the right balance in the system that needs to be optimized globally.

> a) 85th percentile will keep creeping up with each iteration of such speed limit adjustment,

That doesn't actually occur. In 1997, West Virginia raised its speed limits from 55 to 65 mph on limited access 4 lane divided highways. The 85th percentile speed incrased from 62 mph to 66.5 mph. The compliance level with the speed limit went from 15% to nearly 85%. On interstate highways, the speed limit increased from 65 mph to 70 mph. The 85th percentile speed increased from 70 mph to 71.6 mph. The compliance rate went from 50% to about 70%.

In both cases, the compliance rate went up (in one case, substantially). Also, the Martin Parker study [1] also says that lowering and raising speed limits do not substantially affect actual traffic speeds.

[1] https://www.ibiblio.org/rdu/sl-irrel/index.html

> People simply IGNORE the speed limit and drive at what they consider to be a safe speed.

And a lot of people are completely incapable of determining what is actually a safe speed.