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Comment by halosghost | Hacker News Reader

Actually, my dad has a Model S and one of the coolest features is that it actually does scan for speed limit signs and tell you the current speed limit on the dashboard (you can configure a limit over the speed limit for when this should show up).

Now, I have no idea whether or not this feature is utilized for autopilot (though I would kind of assume it would be), but it is there :)

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Is it actually scanning for signs, or is it using map data to determine the speed for the current road segment? I suspect it's actually the latter; reading road signs is a somewhat difficult CV problem, whereas having a well-annotated map is largely a solved problem already. (My old Garmin GPS had this data!)

That's a good question. He is under the impression that it's actually scanning them, but I honestly don't know (I am aware that the mapping data would be much easier to accomplish).

The map is only the start. No map can accommodate all the local changes and rules (small/temp construction zones) nor will local authorities always forward minor changes (school zones).

They very well may be doing the latter as well, but Tesla has specifically said that their camera reads the speed from road signs[1]

[1] http://www.teslamotors.com/blog/dual-motor-model-s-and-autop...

Reading road signs is exceedingly tricky. It's not just the OCR, there's plenty of other gotchas. e.g. what if you miss a road sign because you were overtaking a truck when the sign went past?

Road signs also have situational contexts. e.g. in the UK there are road signs indicating a max speed for an upcoming sharp bend (or series of bends) in the road. There isn't always a matching speed limit sign after the bend because drivers are assumed to work that out for themselves. But will the cars do so? Or will your self-driving car get stuck at the lower speed?

In my jurisdiction the yellow "limit" signs before corners are not actually speed limits, just references. You are allowed to disobey them at your peril. Sometimes that means you can do 80kph around a "30" corner, a common situation on mountain roads.

That also avoids the enforcement problems such as where the new limit should being and end, and the difficulty of measuring vehicle speed through a corner.

> Reading road signs is exceedingly tricky.

You (and parents) vastly overestimate difficulty. They are reflective, high contrast, using known font and very limited symbols (0-9). Car CV systems can distinguish pedestrians from background, they can read a freaking sign.

You have to distinguish the sign from signs on trucks (indicating their maximum speed), reflections of signs in windows, you have to recognize the sub-signs which might limit the scope of the main sign (speed limit might only apply to exit or under certain weather conditions), then there are the usual adverse conditions like rain, reflections, dirt, plants, shadows etc.. Just search for "german traffic sign recognition benchmark" to see what the state of the art is (ConvNet).

It knows where cars and the lanes are. So no it doesn't think there are speed signs in middle of road or on a truck.

Sub signs I'll give you. Don't have any where I live though.

Compared to all the other things it must do reading signs is on the easy list.

Speed limits almost always have repeater signs at regular intervals, particularly when it's not national speed limit. The recommended max speed signs on bends are different from speed limit signs too. If there's not a red circle, it's not mandatory. The exception is national speed limit signs, which would require the car to see if it's a dual carriageway or not so it can switch between 60 and 70.

So can you cause a pile up by putting up a fake road sign with a speed limit of 0 or 1mph and waiting for a Tesla to come along??

It is actually scanning them with the camera.

The MobileEye system in the Tesla (and other manufacturers) has some of the most sophisticated CV software on the road - not just scanning for road signs, but identifying road markings, lane markings, curbs, obstructions, traffic signals, etc.

Actually, most map data _doesn't_ have speed limit data associated with it: http://opendata.stackexchange.com/questions/675/data-source-...

Tesla is most likely using their machine vision system to identify speed limit signs, and then incorporate this data into their mapping data.

When I teach an intro law course I use speed limits to explain why the law is so complex. It's much more than signs. The system you describe appears only informational, the car isn't the one picking the speed. It's a big step for a manufacturer to sell a product that will initiate a speed based on it's own determinations.

Absolutely. Like I said, I'm only aware of that feature being informational; I have no information regarding its use in the autopilot mode :)

I used to have a silver motorcycle jacket (think power ranger). It was great for keeping the sun away, but with a couple lines of tape it would make a great mobile speed limit sign. Every telsa a I pass might suddenly read "Speed limit 15" and slam on the brakes.

The cameras can and do detect if a sign isn't stationary, etc.

For speed limits, the obvious technical problem is knowing when they end, if they apply to your road, or maybe a parallel road or an off-ramp, which is mostly easy for a human to tell, but much harder for a camera.

Even though the camera may be better on average processing all this information than the average human driver, it's an unanswered question, from a legal point of view, who's responsible when the camera is wrong.

Volvo has recently taking a stand proclaiming legal responsibility, but it remains to be seen if that's even a possibility in many nations.

> Even though the camera may be better on average processing all this information than the average human driver, it's an unanswered question, from a legal point of view, who's responsible when the camera is wrong.

There may be some jurisdictions where this is the case, but in most I'm familiar with it is fairly well settled that the human driver of a car is legally at fault if the car is driven in violation of the law, and the human driver of the car is also legally responsible for assuring that all mechanical features of the car are maintained so as to not interfere with the human drivers ability to assure that the car is driven in accordance with the law.

(In many jurisdictions, the manufacturer may have liability for accidents and injury due to manufacturing defects, but that doesn't generally absolve the driver for being responsible for driving consistently with the law.)

But does the camera obey the underlying "Speed safe for conditions" rule in effect in most jurisdictions. (They use this to avoid the possibility of there being no limit should a problem crop up with the signs).

It is very possible to get a speeding ticket well below the legal limit. It isn't common, but where fog/snow/ice/rain are a factor I have seen cops hand them out to idiots. And 'conditions' can include the condition of your vehicle. Driving with bald/track tires in the rain can result in an 'unsafe speed' ticket should a cop see you slide.

Care to go into a little more detail for those of us who are curious what it is that makes speed limit laws so complex?

I don't think it's the traffic law that is complex, but the liability involved. If my car picks its own speed and gets the speed limit wrong, who is responsible?

You could say that the ultimate responsiblity lies with the driver, but taking this position effectively means that all self-driving features are pointless (since this implies that the driver should be concentrating on the driving at all times).

If the responsibility lies (partially, at least) with the car manufacturer, they are going to get a lot of lawsuits thrown at them when it gets the speed limit wrong. Every speeding ticket, every accident where the car was going too fast, etc.

Really? Have you looked at any 'new driver' manuals? I'm reminded of the time I came out of school to see two motorcycle cops hiding behind my jeep, using it as a blind to catch speeders.

"Hey, is it a school day?"

"No, we take a couple days off before exams."

"Oh. It's a good thing then that we haven't ticketed anyone."

"But doesn't the law say 'normal school day'? It is a friday."

"Ya, but your school ain't normal."

In California, a School Zone is in effect when children are around, whether you can see them or not.

Many GPS show the current speed limit (I live in France) and it's pretty accurate. They know when we're next to schools, when there's no explicit sign, when a particular city changed the default speed limit, etc. Who would have imagined 10 years ago that Google Maps photographed all houses? The same happened with speed limits.

The fact that some Sat Nav companies like Tom Tom have so many devices in use, they are able to report traffic in real-time.[1] It wouldn't surprise me if similar averages over a longer period are used to identify speed limits (e.g. What is the mode speed rounded to a multiple of 10, when speeds do not appear constrained by traffic).

[1] https://www.tomtom.com/en_gb/licensing/products/traffic/real...

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