Over the holidays, I was riding with my mother. She got herself a brand new Prius.
On the dashboard, I noticed an icon with the posted speed limit.
My question is: Where is the car getting this information?
Is it embedded in the GPS? Or do one of the cars sensors or cameras read the last speed limit sign on the side of the road?
Thanks.
Probably from a map database.
Most of the GPS mapping apps have this information, and I think that most of the data is crowd-sourced.
For many if not most countries, the data is part of the maps provided by the government itself. And not even only the speed limits; some governments report their fixed radar points. Variable radars get crowdsourced or not, depending among other things on whether this is legal and whether the app’s makers care about legality.
They may also have temporary information:
I’ve been driving in France a lot since last summer and every time there are roadworks with a forced detour, my maps apps get a forced stagepoint. That’s the way the French government has of indicating detours: you’re trying to get “from A to B” and the map itself tells the app “you must go through C”. Drove me crazy until I figured it out, but even though I occasionally need to tell Offline Maps to “ignore stage” it’s more convenient than the Spanish method of not indicating anything: “no, damnit, I can’t go through there, there’s a big hole full of men and machinery where you think we have a four-lane street”.
I just got done driving a brand new Volvo XC90 around Eastern California/Western Nevada for my Christmas vacation, and it had all the fancy tools (such as a radar for keeping you a specific distance behind another car while using cruise control). It was clear that the car has BOTH a database of speed limits, covering a large amount of what I was driving, especially the highways, and the ability to “see” speed limit signs. It also was programmed to use the default limit in California and in Nevada if it had neither available (such as when you start your driving in an area where the database is not complete).
My Garmin has speed limits. But not nearly 100% accurate.
I suspect that data is purchased from Google and other companies doing very detailed mapping and such.
If autonomous vehicles become common. Then there will have to be some very rigid guidelines on how that sort of data is collected and updated. The liabilities could be massive if multi vehicle accidents happen happen due to errors.
The whole concept of autonomous vehicles shifts liabilities on a large scale. The costs to avoid that with up to the minute accurate data may also be a huge liability. Driving safely is an individual responsibility now. Machines driving safely will entail another level of shared investment via taxes to attain and maintain.
My '19 Subaru Forester has a navigation system “powered by TomTom”. It thinks the speed limit on my rural Missouri county road is 65 rather than the posted 55. It also thinks the limit on my one lane private gravel lane is the same. I doubt it would serve as an excuse if I were to be stopped for speeding.
Extreme nit pick ahead!
Priusii are Toyotas, not smart cars.
That is all.
My Honda doesn’t give me speed limits, but the Garmin navigator has the option to avoid detours when I punch in a destination. I’ve never used it, but know that it gets updated traffic info through a radio station channel. Some day I’ll test to see if knows when not to send me down roads that have specific No Left Turn restrictions.
I’ve found at least one spot where Tesla does not have the correct speed limit. Generally they are from map database information. Tesla has hinted that the next major iteration of autopilot will read and recognize standard speed limit signs.
My four-year-old Ford tells me what the speed limit is all the time. The information is derived both from map data and from signs. I know this because it recognises temporary limits and overrides the map data.
My car is fairly high-end and cheaper cars won’t have the forward-facing camera to ‘see’ signs. All satnavs display the limit, but the data can be out-of-date.
My BMW definitely reads the signs since it shows even the extremely low limits in my parking garage at work.
I have thought for years that Teslas and BMWs (i3) read speed limit signs through their cameras.
The indication on the dashboard almost always changes at the exact moment I pass the signs. Also sometimes it misses a sign and then the indication is plainly wrong until exactly the next sign.
My Toyota Yaris has a forward-facing camera that reads speed limit signs. That’s not a particularly high-end vehicle.
I was given a brand new Ford Mondeo to drive around in for work for a few weeks last year. It had the ability to read speed limit signs. I know this because the last 3 miles of my commute home is on a brand new road that didn’t appear on the car’s sat nav map, but it still knew the speed limit.
Anyway, I think the system is flawed - I drove from Bristol to Devon on a 60mph single carriageway road. Almost every side road is limited to 30mph and signed as such. EVERY FREAKING TIME I drove past a side road, the car read the signs and thought the limit had reduced from 60 to 30mph. It made the cruise control almost unusable.
Wow, memory not what it was. It seems I’ve remembered that backwards. The side roads are National Speed Limit (White circular sign with a diagonal black stripe), while the main route (A38) is restricted to either 40 or 50.
Here is an example where the car picks up the national speed limit. The main route is restricted to 40mph here:
Google Maps
Wifes '19 Subaru Ascent is the same. It’s data tied to the GIS road network. It’s an attribute of the road in the database. Other attributes can include things like one way, or gravel road and can be used for fastest routing for EMS.
My co-worker manages this for the county I work for (we use our own data for EMS routing)
On a nation wide scale, it’s not always accurate. Like GaryM, for my Wifes Ascent, the speed limit on the gravel road to our house shows as 50mph. You might be able to hit that speed on a dirt bike if you are a very, very good rider with a death wish.
Priusii are Toyatas, and they are smart cars.
They are not Smart cars.
Another possible complication is the posted signs might not match what the speed limit is supposed to be, “on paper.”
There was a section of road in my town that was posted with 45 mph speed limit signs for at least 20 years, until someone finally (in the written town ordinance) noticed it was actually supposed to be 35. It’s possible the speed limit from the map data is accurate, but the signs are not.
Another rural road I travel goes from 35 to 45mph at a certain spot. The 45mph sign was knocked down by a plow two winters ago and still hasn’t been replaced, so as you drive by the area the GPS speed limit changes there, but there is no sign to agree with it. If you weren’t familiar with the area, you’d probably think the GPS was wrong.
Sometimes even somewhat temporary speed limits are updated on the geographical database.
Construction and road conditions as well.