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Posted limit detection seems reliable in existing cars, both self-driving and not; is there some reason to believe this will be any less reliable than other saf

Posted limit detection seems reliable in existing cars, both self-driving and not; is there some reason to believe this will be any less reliable than other safety technologies?

helen___keller 3y ago
I live in Boston and my car’s HUD displays this information (speed limit and such). Sometimes it gets it wrong despite living in a major city center. Once my car even alerted me when I was going the wrong way on a one-way — except that I wasn’t. I can only imagine in deep suburbs / rural it is even less reliable.
- MarkSweep 3y ago
  Boston can really confuse a GPS. While driving in the underground freeway, the GPS was giving me turn-by-turn instructions for the city streets above.
- wtallis 3y ago
  It sounds like you're describing a system based on GPS and map data, not one of the systems that read the actual signs posted as you drive by them. The only problems I've had with the speed limit sign reader in my car are conditional speed limits (e.g. school zones during certain hours, truck-specific limits). Otherwise, they're just limited by the prevalence of the physical signs.
  - bloaf 3y ago
    Even reading the signs is non-trivial, I drive several stretches of road where an access road runs parallel to a highway, and the 20mph lower speed limit signs for the access road are clearly visible from the highway and only slightly farther off the shoulder than the correct signs.
- jonhohle 3y ago
  This seems like a useful service for cities to provide: street maps and traffic rules for each segment in a standard format.
adrr 3y ago
Its wrong all the time on my Tesla. Its always fun when the autopilot brakes to drop to 55 mph on the freeway when the speed limit is 65.
s1mon 3y ago
Given that GPS gets confused and thinks you're on surface roads when you're on the highway and vice versa, I don't see how this will always work. In dense urban areas there are often multiple layers of roadways going the same direction with very different speed limits. Also basic issues like GPS errors because of tall buildings or foliage cover can easily confuse systems such that you look like you're 100's of feet away from your actual position.
Jtsummers 3y ago
There's a sign indicating the default speed limit in my town, 25mph, with some extra text that anyone who can read will realize it's indicating the default speed and is not a speed limit sign. But otherwise it looks exactly like a speed limit sign, and it sits in the middle of a 50mph zone. Apple and Google Maps both tell me the speed limit is 25mph for about 1/4mile until the next sign indicating 50mph shows up. I have been told it trips up Teslas (but don't have one and haven't driven one here so cannot personally confirm). It'll be fun to have everyone's car slow down suddenly to match this non-existent speed limit, going from 50-60mph down to 25-35mph.
- woodruffw 3y ago
  My understanding is that these systems use a combination of posted sign identification and GPS data.
  - deleted 3y ago
    [deleted]
  - Jtsummers 3y ago
    Right. Here the databases are wrong so the GPS data will indicate 25mph and the sign looks like a speed limit sign so posted sign identification will likely be tripped up (again, based on reports from Tesla owner friends and colleagues). So for 1/4 of a mile on a 50mph road cars that automatically enforce the speed limit will be screwing up. And I doubt this is a unique situation.
    - woodruffw 3y ago
      That sounds pretty unique to me; I've done a few 1000+ mile road trips across the US and have never run into a sign that looks like a speed limit but isn't actually one. The closest thing would be a yellow advisory sign, but those don't look like speed limits. (This sounds like the kind of thing you should report to either your state or county -- AFAIK every state maintains a DB of posted limits with geofences, and correcting them is generally a high priority for ticketing reasons.)
oh_sigh 3y ago
With clear conditions and no obstructions, yes, but my model Y frequently doesn't pick up the right speed limit, because: fog/rain/snow, glare, obstructed by another vehicle, defaced sign, no sign, non standard sign(eg variable speed limit sign in school zone).

Posted limit detection seems reliable in existing cars, both self-driving and not; is there some reason to believe this will be any less reliable than other safety technologies?

helen___keller 3y ago

I live in Boston and my car’s HUD displays this information (speed limit and such). Sometimes it gets it wrong despite living in a major city center. Once my car even alerted me when I was going the wrong way on a one-way — except that I wasn’t. I can only imagine in deep suburbs / rural it is even less reliable.

MarkSweep 3y ago
Boston can really confuse a GPS. While driving in the underground freeway, the GPS was giving me turn-by-turn instructions for the city streets above.
wtallis 3y ago
It sounds like you're describing a system based on GPS and map data, not one of the systems that read the actual signs posted as you drive by them. The only problems I've had with the speed limit sign reader in my car are conditional speed limits (e.g. school zones during certain hours, truck-specific limits). Otherwise, they're just limited by the prevalence of the physical signs.
- bloaf 3y ago
  Even reading the signs is non-trivial, I drive several stretches of road where an access road runs parallel to a highway, and the 20mph lower speed limit signs for the access road are clearly visible from the highway and only slightly farther off the shoulder than the correct signs.
jonhohle 3y ago
This seems like a useful service for cities to provide: street maps and traffic rules for each segment in a standard format.

adrr 3y ago

Its wrong all the time on my Tesla. Its always fun when the autopilot brakes to drop to 55 mph on the freeway when the speed limit is 65.

s1mon 3y ago

Given that GPS gets confused and thinks you're on surface roads when you're on the highway and vice versa, I don't see how this will always work. In dense urban areas there are often multiple layers of roadways going the same direction with very different speed limits. Also basic issues like GPS errors because of tall buildings or foliage cover can easily confuse systems such that you look like you're 100's of feet away from your actual position.

Jtsummers 3y ago

There's a sign indicating the default speed limit in my town, 25mph, with some extra text that anyone who can read will realize it's indicating the default speed and is not a speed limit sign. But otherwise it looks exactly like a speed limit sign, and it sits in the middle of a 50mph zone. Apple and Google Maps both tell me the speed limit is 25mph for about 1/4mile until the next sign indicating 50mph shows up. I have been told it trips up Teslas (but don't have one and haven't driven one here so cannot personally confirm). It'll be fun to have everyone's car slow down suddenly to match this non-existent speed limit, going from 50-60mph down to 25-35mph.

woodruffw 3y ago
My understanding is that these systems use a combination of posted sign identification and GPS data.
- deleted 3y ago
  [deleted]
- Jtsummers 3y ago
  Right. Here the databases are wrong so the GPS data will indicate 25mph and the sign looks like a speed limit sign so posted sign identification will likely be tripped up (again, based on reports from Tesla owner friends and colleagues). So for 1/4 of a mile on a 50mph road cars that automatically enforce the speed limit will be screwing up. And I doubt this is a unique situation.
  - woodruffw 3y ago
    That sounds pretty unique to me; I've done a few 1000+ mile road trips across the US and have never run into a sign that looks like a speed limit but isn't actually one. The closest thing would be a yellow advisory sign, but those don't look like speed limits. (This sounds like the kind of thing you should report to either your state or county -- AFAIK every state maintains a DB of posted limits with geofences, and correcting them is generally a high priority for ticketing reasons.)

oh_sigh 3y ago

With clear conditions and no obstructions, yes, but my model Y frequently doesn't pick up the right speed limit, because: fog/rain/snow, glare, obstructed by another vehicle, defaced sign, no sign, non standard sign(eg variable speed limit sign in school zone).