How is Tesla supposed to determine the speed limit?

[Sonny Daze]

As reported here, and basically confirmed by Elon on twitter, Autosteer's use is now restricted to the speed limit on some roads in some situations (results vary). Some are OK with this some are not. The biggest issue seems to be when the vehicle "thinks" the speed limit is 5 or 10 miles below the actual speed limit, causing the vehicle to quickly reduce speed creating a potential safety issue and in general just being annoying. I've heard all kinds of ways Tesla is supposed to be determining the speed limit but it seems that they are not able to do this consistently. Just how are they supposed to accomplish this?

I'd like to focus on how to implement this change, rather than whether or not it should even be happening, as that has been discussed ad nauseum, but there's allways one (or 10, or 20).

 

[Doug_G]

Autopilot camera reads the signs.

Some GPS systems have the speed limits recorded in their database, and show it on the display, but it's not always up-to-date.

 

[mblakele]

At least some of the problems I've read about don't sound like the simple kind of speed limit error: reading a trucks only 55 sign in a 65 zone, for example. Instead we're hearing about cars on the freeway suddenly dropping the speed limit for a few hundred yards, then picking up again.

I'm speculating, but to me this sounds like it might be due to a transient GPS error. Imagine that you're on a 70 mph freeway, driving 85 because your user setting is +15. Then GPS temporarily places the car on a restricted road (non-freeway), say that 45 mph frontage road parallel to the freeway. That could have a dramatic effect on the car's internal speed limit.

Unfortunately I see GPS errors on this scale pretty frequently, on every phone I've owned. Waze regularly places me one street over from where I really am, and right now the Tesla app thinks I'm trespassing in my neighbor's back yard.

I can think of various ways to try and correct for errors like these, but they won't be foolproof.

 

[Sonny Daze]

From what I can tell, the combination of techniques they may be trying to use is inadequate, and it seems odd to me that they would be altering the vehicles behavior on information they have to know is not consistent. Giving a warning or alert based on inconsistent information is one thing, but decelerating the vehicle seems irresponsible.

 

[NeverFollow]

Autopilot camera reads the signs.

Some GPS systems have the speed limits recorded in their database, and show it on the display, but it's not always up-to-date.

I think that a GPS base system is the ONLY way to determine the correct speed limit:


I live in an area where some major boulevards and arteries have a 25 m/h speed limit, others have a 30 m/h or 35 m/h.
Even in some residential area the speed is limited to 15 m/h.

But it is difficult to locate the speed limit signs especially if you are making a right or left turn into one of those major avenues.

There are also some flashing sign indicating the speed of an approaching car.
The sign is flashing even if the measured speed is below the speed limit.

But I never been able to find any speed signs before, like one block before, those flashing speed signs display.
In the case of multiple lanes, like tree lanes on each side, the flashing sign sign is on the side, instead of been above of each lane.
So it is impossible to know for which car is the flashing speed limit displayed.

Also some streets have several speed bumps but there is no sign to indicate in advance that there will be a speed bump.
There is only a sign just by the speed bump, which I found not sufficient enough to give enough warning.

The speed bump force you to practically stop your car.
It is IMPOSSIBLE to pass a speed bump even when respecting the residential 25 m/h speed limit.
Otherwise you might bump your head on the ceiling of your car &$%#@!!!

I am not also talking about the numerous potholes,
that I doubt would be detected by the Auto Pilot earlier in advance to slow down ?

- Using Autopilot in cities while respecting the speed limit
and also bee able to detect the presence of speed bumps and potholes seems to be very challenging.

 

[BerTX]

My car definitely gets gps-based as well as direct camera observation. Just yesterday as I turned from a 70 mph highway onto one with a 65 mph limit, there was no sign on the second road, yet the recognized limit changed to 65.

I personally have not had the car slow on the highway except in the case where I'm following another car which is exiting and slowing.

 

[MorrisonHiker]

The speed limit recognition still isn't enabled on AP 2.0 cars. When I first got the update on 12/10 which displayed specs on the dash, I thought it was working but after driving to work a couple of times, I realized it was using historical speed limits and not reading the signs. I received the maps update on 12/24 and noticed some of the speed limits have been updated/corrected but many of the newly changed limits are still displayed incorrectly. Since autopilot isn't enabled yet, it isn't much of an issue but the driver does need to be vigilant and ensure they are not exceeding the current speed limit.

 

[thegruf]

My guessimate is that the car primarily uses speed limit data in the Navigon database (which is also used for routing).
It *may* also use speed limit sign recognition, but I have significant doubts about this, or at least how effective this is.
Logically this is the way it must be as the car can hardly go barrelling into a restricted area at highway speed just becasue it didn't see a sign or the sign was dirty.

I suspect this Navigon database contains numerous errors, most comments suggest it is at least a year out of date, so recent limit changes if nothing else are not included.

Albeit I am based in the UK, I have specific (non-divided) roads I use which do not have speed limit markings on them, where the car will slow to 45mph (the limit is 60mph throughout) on certain sections, both straight and curves, very repeatedly.

It can only be doing this with stored data, which is where many of us keep coming back to the fact that it is one thing to adjust the cars speed to the prevailing limit, but another thing entirely to slow the vehicle unexpectedly and without warning due to erroneous data.

With 8.1 apparently imminent I can only hope that Tesla take the oportunity to refine some of the decision making in relation to AP speed management or as an absolute minimum substantially improves the accuracy of database used.

 

[dandelot]

A street near home shows 40MPH limit one way, 45 MPH when driving the other way. Cute, right? What's
a sensitive AI supposed to do with that?
And, too, there is really only one sign each way saying speed limit in the 2+ mile road with several crossing roads.

 

[182RG]

I think that a GPS base system is the ONLY way to determine the correct speed limit:

Unfortunately, that's going to be a real problem in areas that have digital speed limit signs that change speed based on a centralized computerized traffic monitoring/control system. I'm starting to see that a lot more of these.

 

[thegruf]

so called "Smart Motorways" with speeds adjusted to the traffic flow are becoming the norm over here.
I dont use them that much but have never see the Tesla react to a variable speed limit sign, although these are usually on overhead gantries not at the side of the road as above.

It would be a good opportunity for Tesla to publish a blog describing in full how the car behaves regarding speed limits with AP, particulalry as the behaviour is changing from one build to the next

 

[Sonny Daze]

 

[ElectricTundra]

Temporary changes in speed limits isn't unusual here. They'll hang new signs over the old ones and then remove them a week, month, or several months later. Using database info as primary and supplanting it and updating it with local vision should work.

 

[Lump]

Needs a tad bit more work

 

[GTIceman]

I have an issue here in Tampa on 275S where the car thinks it is a 30mph zone and the car will all of a sudden decelerate from whatever I have autopilot set for, usually 70, to 30. Very unsafe.

 

[EVie'sDad]

I was driving on a 45 mph hwy, when we came upon a 30mph sign during a sharper turn, the car completely ignored the warning and remained at the TACC/Autosteer speed assigned. It then changed a 3rd time to 50 mph, all in the span of about 3 minutes. The question is not that Tesla thinks it cannot see the signs, it is if it sees the sign but chooses to ignore it.

IMHO the reason for the reduced speed limit is because the technology (camera/radar/ultrasonics) is not sufficient to always keep the Tesla in it's lane. One minor hill and the hunt mode begins, swerving side to side trying to find the other lane lost when cresting the hill. We really need for the car to maintain direction when in doubt, and restore the +5 mph limit to keep up with the traffic when almost NEVER goes the actual speed limit. To remain at a slower pace is to invite an accident. I fear more such incidents are going to occur because of the reduction in speed restriction.

It is my belief that if the user accepts responsibility, why prevent them from operating the vehicle in the manner of their own choosing? Tesla is not liable in these cases, as it is clearly stated using the technology that ANY AND ALL accidents are the responsibility of the driver, which is why AP is currently Level 2 semi-autonomous, think of it more as advanced driving assistance. It should not be restricting how I can use the vehicle if I am still the one being held accountable.

 

[lunitiks]

Needs a tad bit more work

That's just unbelievable!

 

[Hrhkee]

I had an AP1 loaner on autopilot creating a hill. When the car lost track of the road at the top, it alarmed for me to take control immediately.

 

[Doubletap67]

Needs a tad bit more work

It seems to be responding to the overhead signs.