If the reported speed of 38 mph is correct it does not appear to have been speeding, unless most of the reports have the location wrong, or the speed limit has changed in the last 9 months.

The nearest sign on the road it was on, for the direction it was traveling according to most reports, that it would have passed says that the speed limit is 45 mph [1]. That image is from July 2017.

For the other direction it is 35 mph [2].

[1] https://www.google.com/maps/@33.4350531,-111.941492,3a,75y,3...

[2] https://www.google.com/maps/@33.4371031,-111.9433154,3a,75y,...

If the reported location of not-Seattle is correct, then 38 in a 35 isn't speeding.

(disclaimer: I don't want to be defending Uber, I just don't see the need for the red herring)

FTA: "Nearby signs show the speed limit was either 35 or 40 mph, though the 40 mph sign was closest to the accident site."

Unlike earlier articles, this seems to imply that the SDV was not speeding.

It was going 3mph over the speed limit, a perfectly reasonable speed that is still probably lower than almost everyone else on the road.

Serious question: how are speed limits enforced (or not) in the USA? From what I read on the internet, it seems like they are 90% unenforced, 10% arbitrarily enforced by cops who choose who they want to pull over from the masses who are routinely speeding.

If they are mostly unenforced, how does the system work? Does everyone implicitly add 20% to the posted limit, or do they just go whatever speed feels right to them given the road and the conditions?

(In my part of Australia, speeding is fairly common, but not speed limits are not a joke. You can expect most people to stick within ~5km/h of the limit, and if you choose not to then there's a real chance you'll get done by a hidden camera. The idea of everyone ignoring the limits sounds terrible: of course they are a bit arbitrary, but that's unavoidable for any unambiguous law, and the alternatives of arbitrary enforcement or no enforcement seem much worse.)

> If they are mostly unenforced, how does the system work? Does everyone implicitly add 20% to the posted limit, or do they just go whatever speed feels right to them given the road and the conditions?

Usually people go limit + 10mph on major freeways, and "whatever feels safe" in city driving.

Part of the issue is that within large parts of the united states, speed limits are set at the 85%ile of the speed people drive [1] ... and in my experience, often are only enforced if the police suspect you of something else, or you are driving extremely aggressively (cutting people off, not safe stopping distance, etc.) because speeding is a far more cut-and-dry offense to prosecute, "reckless driving" may be easier to argue away in court due to the level of judgement required.

[1] https://usa.streetsblog.org/2012/11/16/one-for-the-dustbin-t...

That actually really sucks to hear, I was hoping that SDVs would adhere and never break the speed limit. 3 MPH at the forces we're talking about can actually make a difference in life or death.

Waymo discovered sections of Mountain View where "the flow of traffic" was routinely 5-10 mph over the speed limit, and driving at the speed limit was actually more dangerous because it caused human drivers to try and go around the vehicle.

>> it caused human drivers to try and go around

Nope, drivers made that decision on their own. They were not forced into it.

Shouldn’t self driving cars be designed to be as safe as possible in the world they’re actually going to drive in, rather than one where everyone else adjusts their behavior?

Luckily caused isn't the same thing as forced, so you are both correct.

I guess we can call that the trolley paradox.

Sure. 3 MPH would have made a difference. So would 3 MPH less after that, and 3MPH more... heck, if it had been going 2 MPH total she'd probably be fine! In the aftermath of a front collision it would always have been safer if the car had been going slightly slower, regardless of the speed limit.

The strangest part of watching this story unfold has been discovering that some people have faith that speed limits are anything except a rough guess as to what's mostly safe on a given road. Oh, and subtract 10% from that guess to compensate for the fact that human drivers under 60 years old almost all speed by 4-9 MPH.

According to the UK DOT the estimated pedestrian accident survival rate is 55% at 30mph and just 5% at 40mph (due to kinetic energy rather than reaction times) so 3mph in this range is not exactly an insignificant difference. The strangest thing about watching this story is that people who are apparently ignorant of this still feel sufficiently certain of the relative unimportance of speed differences in this range to sneer at other people for commenting on it.

Of course, as others have pointed out, human tendency to ignore speed limits and react badly to vehicles driving slower than ambient traffic speed creates another potential hazard to trade increased accident fatality rates off against when deciding if and when self driving vehicles can speed. It's trolley problems all the way down.

I agree fully with your first paragraph and I chuckled at the "trolley problems all the way down" depiction.

However I can't imagine a car company accepting the legal liability of allowing their autonomous cars to go over posted speed limits to "match traffic".

In a trolley problem you have the option to refuse a decision. By participating in "speed matching" you become one of the trolleys and you have accepted the unsafe conditions.

Oh, I'm pretty sure that self driving software isn't being programmed to systematically disregard speed limits to match traffic, not even by a company with Uber's attitude towards regulations, but it is an example of conditions where rigid adherence to speed limits might increase rather than reduce risk.

With enough self-driving cars on the road (which of course there aren't now), rigid adherence to speed limits might change the safest-and-easiest driving speed for everyone and lead to everyone driving at the limit rather than everyone everyone driving 5mph (or 10mph or whatever) above the limit.

So the safest reasonable thing for self-driving cars to do could depend on how many of them there are around.

(Of course there are other considerations of that sort. E.g., if all cars on the roads were self-driving then they could coordinate with one another in interesting ways and maybe go substantially faster than human-driven cars for a given level of safety. Maybe not, though, because of risks to pedestrians.)

Hmm, turns out Google cars are programmed to go over speed limits in certain situations. Quote from a Reuters article:

Google’s driverless car is programmed to stay within the speed limit, mostly. Research shows that sticking to the speed limit when other cars are going much faster actually can be dangerous, Dolgov says, so its autonomous car can go up to 10 mph (16 kph) above the speed limit when traffic conditions warrant.

https://uk.reuters.com/article/us-google-driverless/look-no-...

I wonder how they decide over what warrants speeding.

> According to the UK DOT the estimated pedestrian accident survival rate is 55% at 30mph and just 5% at 40mph (due to kinetic energy rather than reaction times) so 3mph in this range is not exactly an insignificant difference.

You'd have that range whether people went at the speed limit, above the speed limit, or below the speed limit. As long as speed limits are made with actual speeds taken into account (they are) that argument is irrelevant to whether you should speed. It just means that if you really want to be safe to hit someone you shouldn't go above 25mph, no matter what the speed limit is.

> The strangest thing about watching this story is that people who are apparently ignorant of this still feel sufficiently certain of the relative unimportance of speed differences in this range to sneer at other people for commenting on it.

The speed limit here was at least 40, wasn't it? Your own numbers say that the differences are unimportant above 40.

The police spokesperson is quoted saying the vehicle was doing 38 in a 35mph zone, which is pretty much where the curve suggests an extra little bit of speed is most lethal. (Other reports have suggested other speed limits)

I see this attitude a lot, but it seems strange to me. Of course any hard line will be somewhat arbitrary, but we need to draw hard lines if we want unambiguous, consistently enforceable laws. What's special about speed limits that makes it okay to ignore them?

To me they seem analogous to age-of-consent laws, which of course are not perfectly chosen for every individual -- and of course there's no magical change that occurs on a person's birthday -- but the law reflects society's best judgment of the balance between (protecting the vulnerable and allowing people to make their own choices :: safety and efficiency).

I somewhat agree, I keep fighting this on HN - but speed limits are for two categories of people - the people driving, and the people expecting those drivers to be going a specific speed (or range). And 40 - 50 is not a range that is ever safe to put near people.

I grew up near (in the bay area) Almaden Expy where the signs post 45 (which means that in the bay area the limit is really 55). Just search for "Almaden Expy killed" in google and let me know if that's a safe street.

It's analogous to that, except that speed limits very reliably take the reasonable-balance number and then drop it several mph. It's a feedback loop, where people drive faster and limits are set with driving faster in mind.

You forgot that Ek = 0.5 * m * v² So it is "more dangerous" to be 3 MPH above the speed limit when the speed limit is higher.

I believe it's not clear whether or not it was speeding, From the article, it sounds like it may have been in the middle of transitioning from 35MPH to/from 40MPH.

Going at or below the speed limit would cause autonomous vehicles to be a hindrance to traffic as real humans know that it's safe to exceed the limit by 5-10 mph. If you hard code the vehicles to arbitrarily go exactly the posted speed then adoption will likely be very difficult and it would actually make the roads a more dangerous place to be as normal traffic would need to veer around the car.

The sign (from Streetview imagery in July 2017) shows 45mph.

There was no one else on the road (or, reports haven't mentioned other traffic being a factor).

That doesn't change the fact that posted speed limits are almost always slower than is reasonable. 38 mph is a reasonable speed on all but the windiest of roads.