How does the car know what the speed limit is?

[3sr+buyer]

The speed limit sign in the display can be useful if the driver enters a road and the next speed limit sign is not for a while, but how does the car know what the speed limit is?

Is it through interpreting speed limit signs seen by the cameras? If so, then that has the same limitation as a driver would if entering a road where the speed limit signs are widely spaced.

Or is there some "crowdsourcing" mechanism where the cars report speed limit signs seen to some sort of central database that cars can look up when they enter the road?

 

[father_of_6]

Just a guess... it probably uses a mix of navigation data and computer vision.

 

[valaeyron]

Or is there some "crowdsourcing" mechanism where the cars report speed limit signs seen to some sort of central database that cars can look up when they enter the road?

Yep. There's a secret database that all the cars built since 1982 report to. It's "gubmint" run too, of course. But sshhhhhhh... we don't talk about it openly, erm-kay?

 

[LoudMusic]

It's in the Google Maps data, but it isn't always correct.

 

[Knightshade]

Just a guess... it probably uses a mix of navigation data and computer vision.

WINNER WINNER CHICKEN DINNER!

It does both.

 

[ss71]

Relies heavily on vision in my experience. We have several speed limit changes identified as you see in the photo. Not only is it just the dumbest thing but it means the car does not understand what the new speed is limit when passing this. Frankly, humans don’t either. No idea how this passes DOT guidelines.

 

[drtimhill]

The speed limit sign in the display can be useful if the driver enters a road and the next speed limit sign is not for a while, but how does the car know what the speed limit is?

Is it through interpreting speed limit signs seen by the cameras? If so, then that has the same limitation as a driver would if entering a road where the speed limit signs are widely spaced.

Or is there some "crowdsourcing" mechanism where the cars report speed limit signs seen to some sort of central database that cars can look up when they enter the road?

It's both the nav system database and the car reading speed limit signs. A number of people have tried to figure out which source "wins" if the two have different values, but no-one is sure (it could be as simple as posted signs win, but it might be the lowest speed wins).

 

[sgong6]

Intuitively, the camera reads the road signs. However, when the road sign is not clear, I'm not sure if the map has embedded speed limit information. My Kia does, however.

 

[3sr+buyer]

Relies heavily on vision in my experience. We have several speed limit changes identified as you see in the photo. Not only is it just the dumbest thing but it means the car does not understand what the new speed is limit when passing this. Frankly, humans don’t either. No idea how this passes DOT guidelines.

View attachment 759210

The vehicle code probably specifies a default speed limit for the type of road. In theory, drivers should know what it is (although visitors probably do not, or assume that it is the same as where they are from, not always correctly). But it would still be better just to have a sign showing the new speed limit instead of "end speed limit __").

I did find an error in the speed limit display today. I got on a road with a speed limit of 40mph. It turned into a freeway, where the default speed limit is 65mph (and everyone drives and the highway patrol enforces as if the speed limit were 65mph, since most freeways in the area of 65mph speed limits). But, in the absence of any speed limit signs, the display kept showing a speed limit of 40mph.

 

[father_of_6]

Relies heavily on vision in my experience. We have several speed limit changes identified as you see in the photo. Not only is it just the dumbest thing but it means the car does not understand what the new speed is limit when passing this. Frankly, humans don’t either. No idea how this passes DOT guidelines.

View attachment 759210

Nice, so it tells you what the speed limit ISN'T, instead of what it is?

This sign was designed by the people who made v11.

 

[lexapro]

I live in a coastal city in SoCal, where we regularly drive on 'Pacific Coast Highway' -- even though it is treated like a normal street road in terms of speed limit. Because Tesla thinks it's a traditional highway, it allows AP to drive up to 80mph even when the posted speed limit (and flow of traffic) is 35.

 

[Flybyglass]

It used to be GPS and maps data now not also reads the signs.

 

[jabloomf1230]

Since the car reads both speed limit signs and TomTom-based map speed limit data, the situation can get sticky if there's a conflict between the two sources. It seems like the logic is to use road sign data and fall back to map data.

Which brings me to a pet peeves. Why is road mapping data like a game of whack-a-mole? Shouldn't each country maintain an online database of road mapping data and publish any changes monthly? Right now, vehicles rely on private mapping vendors to somehow figure out what the government is doing. Imagine what would happen if the government decided to opt out of aviation mapping?

 

[Knightshade]

Since the car reads both speed limit signs and TomTom-based map speed limit data, the situation can get sticky if there's a conflict between the two sources. It seems like the logic is to use road sign data and fall back to map data.

Which brings me to a pet peeves. Why is road mapping data like a game of whack-a-mole? Shouldn't each country maintain an online database of road mapping data and publish any changes monthly? Right now, vehicles rely on private mapping vendors to somehow figure out what the government is doing. Imagine what would happen if the government decided to opt out of aviation mapping?

Which government?

Some speed limits are set by the federal government- but relatively few.

Some are set by state governments, there's 50 different ones.

Some are set by counties or municipalities, of which there are tens of thousands


And that's just in the US.

 

[jabloomf1230]

Which government?

Some speed limits are set by the federal government- but relatively few.

Some are set by state governments, there's 50 different ones.

Some are set by counties or municipalities, of which there are tens of thousands


And that's just in the US.

Federal government. There is already coordination of this type in the US. There just isn't a database. For example, my rural town maintains it's own roads. But it can't just change the speed limit on a road if it feels like it. The process is quite detailed and if you're really interested you can read more about it here:

FAQs • How Do We Get the Speed Limit Changed?

ontariocountyny.gov

But there's no requirement that NY State maintain a public database of changes. NYSDOT actually has ArcGIS coverages of all the State's roads and I imagine most US state DOTs do too. That's probably where Google, TomTom, etc. get their updates. All am suggesting is that this process be streamlined and mandated. As more vehicles need this information for navigation, the need will intensify.

 

[charlieaf92]

Some cars are 100% computer vision. As others pointed out it appears that Tesla uses a hybrid approach. My guess would be it prioritizes TSR (traffic sign recognition) and then uses embedded GPS map data as a fallback.

 

[Knightshade]

Federal government. There is already coordination of this type in the US. There just isn't a database. For example, my rural town maintains it's own roads. But it can't just change the speed limit on a road if it feels like it. The process is quite detailed and if you're really interested you can read more about it here:

FAQs • How Do We Get the Speed Limit Changed?

ontariocountyny.gov

But there's no requirement that NY State maintain a public database of changes. NYSDOT actually has ArcGIS coverages of all the State's roads and I imagine most US state DOTs do too. That's probably where Google, TomTom, etc. get their updates. All am suggesting is that this process be streamlined and mandated. As more vehicles need this information for navigation, the need will intensify.

The problem is the federal government can't compel the state governments to report local road data up to them.

They can offer bribes (tax/grant incentives) to encourage that- but they can't require it.

Same issue exists with the NICS criminal background check system... SOMEBODY has all the criminal records out there, it's just a ton of different somebodies that you can't compel to work with each other to feed one central federal database.


I mean, I agree it'd be great if there was a single, always accurate, database covering all this info- but there's reasons there isn't, and thus reasons google and tomtom and others spend so much building their own.

 

[jabloomf1230]

The problem is the federal government can't compel the state governments to report local road data up to them

I know, legislation is needed. It might have to condition federal highway aid on participation in a new program.

 

[Twiglett]

The speed limit sign in the display can be useful if the driver enters a road and the next speed limit sign is not for a while, but how does the car know what the speed limit is?

Is it through interpreting speed limit signs seen by the cameras? If so, then that has the same limitation as a driver would if entering a road where the speed limit signs are widely spaced.

Or is there some "crowdsourcing" mechanism where the cars report speed limit signs seen to some sort of central database that cars can look up when they enter the road?

Sea turtles mate
May as well be for the accuracy in this area

 

[father_of_6]

It's valuable data, so better to let private companies collect it and make a profit than the gov't to spend LOTS of tax dollars collecting it in the least efficient way.