[tallpapab]

Interesting article. One can easily notice that most folks seem to treat the speed limit as a minimum speed rather than a maximum speed. It's not just designers designing for speed. They do so because of market demand. That demand is boosted by advertising - both overt and culturally pervasive imagery. Buckle up folks. Try not to speed. You're really not saving much, if any, time. Also minimize left turns and lane changes. When you do turn (or change lanes) always use your turn indicator. When cars are robots they can do these things. The worry it that freedom loving consumers will still choose thrills over safety and this may stunt the adoption of robocars.

[u801e]

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

That's because the speed limit doesn't match actual traffic speeds. On highways/motorways, traffic typically will freely flow at speeds ranging from 75 to 85 mph (120 to 140 km/h). Posting a speed limit of 55 to 65 mph (90 to 110 km/h) will result in traffic treating those numbers as a minimum acceptable speed.

In fact, in the state of Virginia (in the USA), they have signs posted on their interstate highways that state that commercial vehicles may not use the left most lane if being operated below the posted speed limit (65 or 70 mph).

[dTal]

Surely this is tautological? People don't obey the speed limit because the speed limit doesn't match the speed they're going at?

[u801e]

No, it really isn't. The compliance rate increases when the speed limit is set to the upper limit of the pace speed/85th percentile speed. I noted some examples[1] in my other post

[1] https://news.ycombinator.com/item?id=16305560

[rootusrootus]

Cars are actually quite safe if you consider how much we use them. Your odds of dying in a car accident are quite low. Given that robocars have their own trade-offs, I don't think it's too surprising that some people will elect to continue to buy human-driven cars indefinitely if given the choice.

[kazagistar]

My odds of dying in a car are much higher then almost anything else in the short term. If there is anything to rationally optimize for, it is car safety.

[rootusrootus]

I think maybe you are missing a whole bunch of other risks in your life that are more likely to take your life.

How much do you worry about dying from a fall, or poison, or alcohol, or drugs? Or a firearm? All of those are either similar to or more likely than dying in a car accident.

If you want to rationally optimize for something that will improve your survival odds, heart health is by a vast, vast margin a better place to spend your efforts.

If you drive an average number of miles per year, you will probably be involved in some kind of accident once every decade. The odds you will die in that accident are pretty low, as it only happens about once every 100,000,000 miles driven.

[icc97]

They may be 'safe' for the people in the car, but not for the people who get hit.

It's cars crashing into bicycles, pedestrians or buses (causing the buses to avoid them and crash) that are the major issue.

The people who die in car crashes are innocent healthy people. Often killed by people who never think how dangerous cars are and assume that they themselves are safe.

One of the major bus crashes [0] was caused by a drunk SUV driver over taking a bus too fast in the rain, losing control, crashing into the bus and killing numerous passengers. The SUV driver only suffered slight injuries.

[0]: https://en.m.wikipedia.org/wiki/Benalm%C3%A1dena_coach_crash

[bsder]

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.

[Piskvorrr]

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.

[snowpanda]

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.

[TeMPOraL]

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.

[u801e]

> 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

[KozmoNau7]

> 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.