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Comment by rootusrootus | Hacker News Reader

They had to use older Teslas to make this work, because newer models don't use sign-reading to determine speed limit.

Abstractly, it's interesting, if only because it probably wouldn't trick a human -- everyone would see the 85mph as BS regardless of the defaced sign.

Has anyone hacked into openstreetmaps yet and fiddled with speed limits?

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Hacked into openstreetmaps? Not necessary, they publish helpful instructions right on their wiki on how to edit speed limits:

https://wiki.openstreetmap.org/wiki/Speed_limits

I do know of one instance where modifying street signs tricked humans: there's a short speed-trap section of road outside a rural town north of me that's labeled 25 mph even though the approach roads are 45 mph. Apparently it's zoned residential even though there are only like 5 houses set way back from the road (looks like it should be 45, maybe 35). Seems like someone in the 70s thought that zoning something for higher density caused high-density housing developments to arrive.

Of course, this section was where the cops liked to sit. When I was in high school, some kids pulled legitimate signs off a different section of road and re-labeled it 45 mph. While the average speed of traffic to school in the morning sped up dramatically for a couple weeks, the police did not agree that the presence of these signs changed the speed limit on the road. Fortunately, the perpetrators got off with a slap on the wrist, unfortunately, the county didn't review and revise the speed limits.

>the police did not agree that the presence of these signs changed the speed limit on the road

Now this would be an interesting legal challenge. The official wording will vary by state but it'll be something like

"a person must not, when the sign is in place on the highway, drive or operate a vehicle on a highway at a greater rate of speed than that indicated on the sign for that category of motor vehicle, unless another sign on a specific highway in the defined area so indicates"

So... can you really be faulted if there's a not-obviously-fake speed limit sign? If I got a ticket for that I would definitely be disputing it.

They literally unbolted the 25 mph signs and dumped them in the ditch... I think there was still a "speed limit reduced ahead" sign.

You'd have a pretty easy case, I think, the only defenses would be "there's a sidewalk here so that's typically 25" and "you drove here before so you should remember it's 25".

Yes ... the older Teslas have the MobilEye chipsets which use this technology. Many other cars use the same MobilEye chipsets today .. so potentially could be an issue in other cars as well.

Its likely now that this error was pointed out that Tesla may add some speed limit validation code to ensure a car doesn't speed up much when a speed limit jumps by more than 25% or something like that..

It only works when this is the first sign TACC sees. If TACC was previously engaged and saw other signs previously, the exploit doesn’t work. I’m sure Tesla fixed this, but given the nature of the edge case, it wasn’t simply a matter of sanity checking.

Why would it only work if it is the first sign?

Maybe because they were probably already doing sanity checking, but the kind that relied on some previous context? That seems reasonable, I’m sure they’ve thought about this kind of attack before, missing an obscure edge case.

This is completely irrelevant, but 85 and BS are the same in LCD 7-segment display text

What do the newer models use? I tried to Google for it, but just kept stumbling on news articles about the OP.

"Front-facing cameras detect speed limit signs on AP1 vehicles and display the current limit on the dashboard or center display. Limits are compared against GPS data if no signs are present or if vehicle is HW2 or HW2.5"

https://en.wikipedia.org/wiki/Tesla_Autopilot#Speed_assist

From what I've gathered elsewhere, the GPS data is OSM.

My understanding is the limits come from OSM. They seem to be relatively accurate, at least in my area. The display doesn't always change exactly where the sign is, and sometimes it's off by a quarter mile, but usually it's closer than that.

Isn't sign reading necessary for say, construction areas, that would have a lower speed limit? If so, researchers could do the same thing by placing false construction signs.

It might be necessary for higher level self-driving, but AFAIK Tesla isn't doing that due to patent issues. Autopilot is just very fancy cruise control, and you're supposed to be in charge. You'd be expected to change the cruise control set point manually when you enter a construction area.

But at least the software could assert that the construction speed was lower than what the map stated the speed limit was so you could only slow down a car which would hopefully be a safer failure.

Cars slowing down when they shouldn't be can create dangerous situations, though I'd agree it's relatively safer when compared to speeding (particularly in residential areas, or roads not made for faster travel).

This is actually one of my biggest gripes with autopilot. It's aggressive at following reduced speed limits, even when traffic is not. I don't know the solution, since the speed limit really does drop to 25-35 mph in a couple spots in our local freeway interchange, but traffic flows through at 55-65 mph all day long, and having the car suddenly brake to 30 mph is unexpected. If there's one thing you want to be on the road, it's predictable. It's when you deviate that accidents happen.

It still is a little bit unnerving that older models can accelerate based off of speed limit signs alone. That seems like a dangerous approach.

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