Local automotive writer Dan Wiese was evaluating the new Acura TLX when he passed a sign for “HWY 100” (Manchester Rd. to locals) and the car helpfully informed him the speed limit was 100 MPH! I wonder how it might’ve reacted to HWY 340?! (What’s that? The speed limit is almost half the speed of sound?) A case of reading but not comprehension. 2021 Acura TLX
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Do they give AI an IQ test? 
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my Honda was picking up some ridiculous speed limits “recognized by AI” from time to time, yet ignoring some clearly readable speed signs… oh, well… as long as it is “assist” only, I don’t care much
Would that be an AIQ test? I was also thinking about a self-driving vehicle “reading” signs and deciding the speed limit was some ridiculous number. Those things have enough accidents as it is.
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The highest highway number I can think of is 694, north of the twin cities, speed limit 55, lucky if you can go 35 many times.
Highway 101 runs right by here, the state patrol acadamy is further up the highway so even if your Acura told you the speed limit was 101 i’m fairly sure the WSP would say otherwise.
Some of the late model vehicles that I road test display the speed limit in the instrument cluster or on the windshield if equipped with heads-up display. The information is based on location and the data in the navigation unit. Sign recognition would have an advantage in a construction zone but without orange signs/cones there should be a reasonable correlation between posted signs and known data. If the egg heads can’t get this right it seems that we are years away from autonomous vehicles.
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My Iphone GPS knows the speed limit. I wonder why it’s not using that instead of trying to read the signs. This is obviously a bug that is very solvable. Computers reading and comprehending text accurately has been going on for years.
About a week ago, I was driving on a road where the local P.D. has erected one of those “Your Speed Is” displays that contains its own radar unit. I was the only car on the road at that point. As I approached it it told me that my speed was 118 mph!
I glanced at my speedometer, and it displayed 45 mph. My GPS displayed 43 mph, which was probably more accurate than my speedometer.
As I got very close to the speed display, it told me that my speed was 38 mph, even though my GPS still displayed 43 mph.
So much for that “Your Speed Is” technology.
And that’s why I dislike speed cameras. You can’t trust their accuracy. Years back one in Florida apparently clocked a palm tree at 90mph.
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I don’t know about a speed camera but a radar gun the officer was using If I remember right { I was living in Florida Then } a guy went to court to contest a speeding ticket after hearing both sides of the argument the judge told the officer to get his radar gun and meet him outside they clocked a tree in front of the courthouse { I don’t remember the speed } but the tree was going much faster than it should have been.
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I wondered some of the same things. First, OCR ought to be good enough to tell the difference between “HWY” and “MPH.” My wife suggested the car might have thought the 100 was kilometers, LOL. And anyway, AFAIK speed limit signs don’t have “MPH” before the number, at least not that I’ve ever seen. Second, the sign reading feature ought to be connected to Nav data, a when-in-doubt backup. The highest speed limit in the US is 85 MPH on Route 130 in Texas. Maximum posted speed limits by state
In this instance, the guy was probably in the outer suburbs of St. Louis and common sense would tell you the speed limit couldn’t be much more than the 40 MPH posted. But clearly “common sense” isn’t easy to program.
As I said…it’s a bug and easily fixable.
If the speed limit is available through GPS then there’s no need to read the speed limit signs.
Common Sense is LOGIC. Computer programming is mostly LOGIC. So yes it’s easy to program in. Logical decisions are exactly what computer programming is all about.
If you ever get a ticket from a system like that and want to beat it, have your attorney demand the calibration records for the speed trap instruments. Maybe they weren’t careful about calibration in your case since they weren’t handing out citations.
Today, that same “Your Speed Is” sign told me that my speed was 25 mph, even though I was driving the limit of 35 on that stretch of road. Luckily that sign can’t issue tickets.
Bug yes, easily fixable, maybe or maybe not. It should, however, be possible to have the system default to GPS data. I haven’t written code in years but believe it or not I do know something about computer programming. “Common sense” isn’t just about logic, it’s also about a certain body of knowledge and the ability to combine bits of information. There’s an old Jim Croce lyric that goes like this: “I was just getting ready to get my hat when she caught my eye and I put it back.” What did he “put back”? His eye or his hat? Straightforward yes/no logic can’t figure it out, which is why true AI is always at least a decade away.
TBH, I haven’t noticed any local “Your speed is” signs being off by a whole lot. Sure, it takes a few seconds to settle on a reading as you approach, kinda like how bathroom scales “bounce” at first. And sometimes the sign appears to be showing the speed of the guy behind you (at least that’s my explanation) but for the most part they seem to be fairly accurate. I know from watching my GPS that the speedometer in my Corolla reads 1 MPH high at pretty much any speed (i.e., 31 at 30 MPH, 61 at 60 MPH, etc.) and those “Your speed is” signs tend to confirm it.
“Houston, we have a problem.”
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“I can’t do that, Dave.”
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Yes. 
Trouble is, it’s not really common sense that’s the problem. If the computer knows the sign says HWY, it will not assume the number is the speed limit. The problem is in the vision systems, which are still not as good as human eyes. Even something as dumb as the right arrangement of shadows can make the computer not perceive what it’s looking at properly. The logic is fine, but because the vision isn’t perfect, it’s a case of GIGO.