# Cruise control - Random braking and speed reductions... anyone else?



## Misanthropic Mike (May 17, 2019)

First off, I really wish Tesla would offer just ordinary cruise control so that I don't have to continually monitor my speed while cruising on the highway, because the "active" cruise is unusable in it's current form. It randomly changes it's setpoint while I'm cruising on the freeway, making my car suddenly decelerate for no reason. It's not only annoying, it's dangerous. Today on the way to work it just suddenly changed from a setpoint of 73 mph to 30 and began braking hard. This happened in broad daylight and good weather when there were no other cars for several hundred yards in front of me (not that it'd be OK for it to do this in any conditions). As a separate issue, it will frequently (like perhaps once or twice per mile) slam on the brakes while I am overtaking other vehicles in adjacent lanes, presumably because the software thinks the adjacent cars might be moving into my lane (they aren't). 

As it stands, I really can't use cruise control at all without being seriously annoyed (and no doubt annoying the other cars around me), meaning my 2019 tesla has less automation than my 1989 honda accord had. I'm praying this is mostly due to my firmware version (2019.7.105) and the relative newness of HW3.


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## MelindaV (Apr 2, 2016)

sounds like your area has google map issues with adjacent low speed roads being picked up from the freeway. watch what the "speed limit" at the upper right corner shows when it is slowing down. If it is not correct to the actual limit, send the correction to Google Maps.


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## Frully (Aug 30, 2018)

The current iteration doesn't read speed signs - it responds to geographic data baked into the map. It's likely that map data was generated when there was a construction zone or the like on that highway and hasn't been updated.

Aside: this is why the self-driving future can't rely heavily on historical data and rather wants a reactionary vision-based AI. Out of date info causes problems.

Until they update AP/cruise to use the camera to read the signs, use the bug report feature to raise the concern about the map segment.
-Activate the voice prompt and say (in one sentence) "bug report: speed limit incorrect on xyz road" (optionally add "is 30mph instead of 65mph")

I've had several map segments in my area fixed this way.


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## Misanthropic Mike (May 17, 2019)

When I looked down, the speed limit in the upper corner indicated 55, which is correct for this road.


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## MelindaV (Apr 2, 2016)

73?


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## MJJ (Aug 7, 2016)

I've experienced this behavior, at the exact same place, day after day (older s/w versions) and now to a lesser degree (severity and frequency, but still extant). I've bought into the map error theory, but if the map has been fixed, there should be NO symptom, not just LESS symptom.

But as to your thread title, not to worry, it's definitely not random


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## Technical48 (Apr 29, 2018)

This is exactly why I'm glad I didn't pay 5kUSD for EAP (or 2kUSD when it was on sale). There really needs to be an option to disable TACC until such time that it becomes less useless.


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## 19Model34me (Apr 5, 2019)

100% agree, I am very disappointed I can’t use TACC because it always hits the brakes. I use cruise control everywhere, now I don’t have it at all. FSD is a pipe dream if you can’t make cruise work.


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## sduck (Nov 23, 2017)

TACC works perfectly for me. I use it all the time. It's not the car, it's the maps in your area.


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## Misanthropic Mike (May 17, 2019)

73 is less than the average speed of traffic on this road.

Jeff Foxworthy once said: "If the speed limit on the highway is 55 mph, you're going 80, and everybody is passing you, you live in New England".

He nailed it.


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## Misanthropic Mike (May 17, 2019)

sduck said:


> TACC works perfectly for me. I use it all the time. It's not the car, it's the maps in your area.


Isn't that a bit like saying "it's not the phone, it's the software"... I'm not sure there is any real difference these days. To put it another way, none of my other cars have this problem despite the existence of these maps.

This leads me to my next idea... until such a time as Tesla is able to make these advanced features work universally and reliably, perhaps there should be a way to disable them. As such, the car will at least be prevented from having less capability than a 90's Toyota. The user can keep track of where it does and doesn't work and activate it appropriately.


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## Olds442 (Dec 12, 2018)

i have the issue on a couple roads that have frontage roads, where it's reading the speed limit on the frontage when i'm in the fast lanes. other than that, no issues here. 
and as silly as this may sound, we use summon all the time so i am glad i ponied up for it. nav on ap works fine as well but i'd probably be fine with basic ap and not miss nav on ap. sorry to hear people are having issues.


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## garsh (Apr 4, 2016)

Misanthropic Mike said:


> Isn't that a bit like saying "it's not the phone, it's the software"... I'm not sure there is any real difference these days.


Yep, especially given that we rely on Tesla to update map information.

I'd feel a lot better about our chances of seeing FSD soon if Tesla would concentrate on fixing these kind of long-standing Autopilot issues. Whether it's due to incorrect map data, or possibly Autopilot misinterpreting a change in road surface as some kind of barrier (I get slowdowns on the interstate when approaching a bridge with a concrete top coat when the rest of the roadway is darker asphalt), these sudden, unnecessary slowdowns are a huge pain to deal with.

The car will always slow down as I approach this bridge in particular (image taken from Google Streetview - construction is long done).


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## sduck (Nov 23, 2017)

Misanthropic Mike said:


> Isn't that a bit like saying "it's not the phone, it's the software"... I'm not sure there is any real difference these days. To put it another way, none of my other cars have this problem despite the existence of these maps.
> 
> This leads me to my next idea... until such a time as Tesla is able to make these advanced features work universally and reliably, perhaps there should be a way to disable them. As such, the car will at least be prevented from having less capability than a 90's Toyota. The user can keep track of where it does and doesn't work and activate it appropriately.


Well, yes, of course. But I thought it would be appropriate to throw that in, as it seems some areas have better maps than others. I wonder how many areas are like yours with lots of problems - whether it's more or less the case than not. And of course I've experienced phantom braking for what must have been a map error - had a few in Texas last week. But around here, it's always caused by bridge shadows and surface changes, and the latter only rarely.


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## Mr. Spacely (Feb 28, 2019)

_"Cruise control - Random braking and speed reductions... anyone else?"_

No. Mine works great.


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## nonStopSwagger (May 7, 2018)

Frully said:


> Until they update AP/cruise to use the camera to read the signs, use the bug report feature to raise the concern about the map segment.
> -Activate the voice prompt and say (in one sentence) "bug report: speed limit incorrect on xyz road" (optionally add "is 30mph instead of 65mph")
> 
> I've had several map segments in my area fixed this way.


Did tesla get back to you after you had the maps fixed using bug reports? The "bug report" feature does not send any data to tesla. It just saves it in a log in your car, which might get download and reviewed (its up to the service tech) when you go to a service center.


__
https://www.reddit.com/r/teslamotors/comments/b67223


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## TomT (Apr 1, 2019)

Yep, frequently.

_"Cruise control - Random braking and speed reductions... anyone else?"_


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## jsmay311 (Oct 2, 2017)

This happens to me too. (Discussed here: https://teslamotorsclub.com/tmc/threads/random-tacc-max-speed-decreases.127189/#post-3530170)



MelindaV said:


> sounds like your area has google map issues with adjacent low speed roads being picked up from the freeway. watch what the "speed limit" at the upper right corner shows when it is slowing down. If it is not correct to the actual limit, send the correction to Google Maps.





Misanthropic Mike said:


> When I looked down, the speed limit in the upper corner indicated 55, which is correct for this road.


It wasn't a speed limit issue in my case either.


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## Long Ranger (Jun 1, 2018)

jsmay311 said:


> This happens to me too. (Discussed here: https://teslamotorsclub.com/tmc/threads/random-tacc-max-speed-decreases.127189/#post-3530170)
> 
> It wasn't a speed limit issue in my case either.


In your TMC post you say it happens at a freeway interchange. TACC can temporarily reduce your set speed at interchanges even if the speed limit doesn't change. From the manual:

When enabled while on a highway interchange or off-ramp, Traffic-Aware Cruise Control may reduce your set speed in 5 mph (5 km/h) increments - to as slow as 25 mph (40 km/h) - to better match the reported speeds of other Tesla vehicles that have driven at that specific location. To override this and continue cruising at your set speed, tap the accelerator pedal or touch the plus (+) or minus (-) button on the touchscreen. The new set speed is maintained for the duration of the interchange or off-ramp (unless you override it or cancel Traffic-Aware Cruise Control). After the interchange or off-ramp, the set speed may revert or change as necessary based on the new location. For example, if you merged onto a different highway, the set speed reverts back to the set speed that was in use before driving on the interchange.


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## Klaus-rf (Mar 6, 2019)

I see it randomly also. This aftn I was at least 50 meters from a car that pulled out from a stop street into my lane on a curve. Then accelerated briskly so I was never closer than the 50 meters. Car panicked with a nose dive braking mode for a second or so. Then went back to the speed limit as if there was no issue at all.

Random and erratic.


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## Craig Bennett (Apr 6, 2016)

I’ve seen degradation in TACC behavior similar to what you are describing in the last several releases. This is especially true when changing lanes. I see no known reason - shadows, other cars, birds, ghosts, anything!

The pattern seems to be that a regression seems to last several iterations before it gets addressed, at which time a new regression sometimes gets introduced.

This is the price of rapid new feature introduction. I generally don’t use a particular feature until I see enough feedback from other users that it appears stable.


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## Olds442 (Dec 12, 2018)

Olds442 said:


> i have the issue on a couple roads that have frontage roads, where it's reading the speed limit on the frontage when i'm in the fast lanes.


i was on one of those roads yesterday that i posted about above, Palatine Road in Arlington Heights, and it read the correct speed for the fast lanes this time. it's the first time it's done that and i drive on that stretch often.

kinda eerie since i just posted about it and now it's fixed, cue the twilight zone music.


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## Kimmo57 (Apr 10, 2019)

Misanthropic Mike said:


> First off, I really wish Tesla would offer just ordinary cruise control so that I don't have to continually monitor my speed while cruising on the highway, because the "active" cruise is unusable in it's current form. It randomly changes it's setpoint while I'm cruising on the freeway, making my car suddenly decelerate for no reason. It's not only annoying, it's dangerous. Today on the way to work it just suddenly changed from a setpoint of 73 mph to 30 and began braking hard. This happened in broad daylight and good weather when there were no other cars for several hundred yards in front of me (not that it'd be OK for it to do this in any conditions). As a separate issue, it will frequently (like perhaps once or twice per mile) slam on the brakes while I am overtaking other vehicles in adjacent lanes, presumably because the software thinks the adjacent cars might be moving into my lane (they aren't).
> 
> As it stands, I really can't use cruise control at all without being seriously annoyed (and no doubt annoying the other cars around me), meaning my 2019 tesla has less automation than my 1989 honda accord had. I'm praying this is mostly due to my firmware version (2019.7.105) and the relative newness of HW3.


My thoughts exactly


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## M3OC Rules (Nov 18, 2016)

I use TACC and autopilot pretty much every time I drive. I have phantom breaking occasionally because of people crossing a long ways ahead, overpasses, and incorrect speed limits. I know where the speed limits are wrong and verified they are coming from Google Maps. I don't use autopilot in those locations and use TACC by itself which isn't affected in my experience. I agree it's annoying and could potentially be dangerous but it's not so much that it stops me from using it all the time. I'm starting to think this is one of their biggest problems right now though. When you're driving its one thing but its especially bad for a passenger. I think it has really soured my wife on the car. We were just at a party with a couple with a Model 3 and they have the exact same situation. The guy drives the car and his wife doesn't want anything to do with it because of Autopilot and phantom breaking. Now this is what they tell other people when they talk about the car. Not the greatest sales pitch. And there are clearly people who drive the car regularly who are complaining here.

It seems like this should be a high priority at Tesla but it doesn't seem like it is. I would much rather have no phantom braking and accurate speed limit detection than NOA. I like watching the sausage get made but at some point I want to eat the sausage.


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## mswlogo (Oct 8, 2018)

M3OC Rules said:


> I use TACC and autopilot pretty much every time I drive. I have phantom breaking occasionally because of people crossing a long ways ahead, overpasses, and incorrect speed limits. I know where the speed limits are wrong and verified they are coming from Google Maps. I don't use autopilot in those locations and use TACC by itself which isn't affected in my experience. I agree it's annoying and could potentially be dangerous but it's not so much that it stops me from using it all the time. I'm starting to think this is one of their biggest problems right now though. When you're driving its one thing but its especially bad for a passenger. I think it has really soured my wife on the car. We were just at a party with a couple with a Model 3 and they have the exact same situation. The guy drives the car and his wife doesn't want anything to do with it because of Autopilot and phantom breaking. Now this is what they tell other people when they talk about the car. Not the greatest sales pitch. And there are clearly people who drive the car regularly who are complaining here.
> 
> It seems like this should be a high priority at Tesla but it doesn't seem like it is. I would much rather have no phantom braking and accurate speed limit detection than NOA. I like watching the sausage get made but at some point I want to eat the sausage.


TACC is where Phantom braking is coming from. It's the "Traffic Aware" part that has a head cold some days.

In my experience wrongs speeds, limited speeds and most "incidents" ahead are handled fairly smoothy.
When the system thinks it's gonna hit brick wall on the highway, it's pretty scary. It decelerates, out of no where, about as fast as my Performance can accelerate.

Occasionally a severe cutoff will hit brakes fairly hard too, but that in some cases is more or less correct, even thought it sometimes overreacted more than I would have.
If someone cuts you off and is accelerating away it sees that and doesn't slow down at all. Pretty impressive.


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## Misanthropic Mike (May 17, 2019)

This morning it happened in a different spot, but I noticed that the nav map displayed my current section of road in red, indicating a traffic jam (there was no traffic jam, cars were flowing smoothly at about 75 mph). There might have been a jam there 15 minutes earlier and the map hadn't updated yet. Could it be that it initiates these slowdowns based on recent traffic information? Isn't that what the cameras and radar are for?


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## mswlogo (Oct 8, 2018)

Misanthropic Mike said:


> This morning it happened in a different spot, but I noticed that the nav map displayed my current section of road in red, indicating a traffic jam (there was no traffic jam, cars were flowing smoothly at about 75 mph). There might have been a jam there 15 minutes earlier and the map hadn't updated yet. Could it be that it initiates these slowdowns based on recent traffic information? Isn't that what the cameras and radar are for?


That's a great observation. I'll have to watch for that.


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## Jay79 (Aug 18, 2018)

Been happening to me more frequently since the new update, it sporadic though. Sometimes AP works flawlessly and sometimes not so much. It actually missed my exit last night on route to a supercharger. I was showing off to a girl I had in my car so I'm thinking my Tesla was getting jealous


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## jsmay311 (Oct 2, 2017)

Long Ranger said:


> In your TMC post you say it happens at a freeway interchange. TACC can temporarily reduce your set speed at interchanges even if the speed limit doesn't change. From the manual:
> 
> When enabled while on a highway interchange or off-ramp, Traffic-Aware Cruise Control may reduce your set speed in 5 mph (5 km/h) increments - to as slow as 25 mph (40 km/h) - to better match the reported speeds of other Tesla vehicles that have driven at that specific location. To override this and continue cruising at your set speed, tap the accelerator pedal or touch the plus (+) or minus (-) button on the touchscreen. The new set speed is maintained for the duration of the interchange or off-ramp (unless you override it or cancel Traffic-Aware Cruise Control). After the interchange or off-ramp, the set speed may revert or change as necessary based on the new location. For example, if you merged onto a different highway, the set speed reverts back to the set speed that was in use before driving on the interchange.


(1) It's not really that kind of an interchange. There are no curves anywhere near sharp enough to warrant a reduction in speed and no one slows down while driving through it.

Here's a map view of the section where the errors occur:









(2) More to the point, I drove through it again last night and paid close attention to the screen, and the speed limit sign on the screen actually disappears for a split second each time the set speed changes. So the problem it does appear to be driven by a problem with the speed limits, but it's apparently _missing_ data rather than incorrect speed limits that are causing the problem.

I submitted a bug report at the time to report the problems with the speed limit.

But I still don't get why having no speed limit data for a very short section of highway should result in a change to the cruising set speed in TACC. And since it's a limited-access divided highway it shouldn't affect set speeds in AP either.


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## M3OC Rules (Nov 18, 2016)

jsmay311 said:


> (1) It's not really that kind of an interchange. There are no curves anywhere near sharp enough to warrant a reduction in speed and no one slows down while driving through it.
> 
> Here's a map view of the section where the errors occur:
> View attachment 26506
> ...


The data comes from Google. You can file a bug report to them.(Menu->Send Feedback) When you do that it makes you click on the section of road where the error is. I tried this on a long freeway entrance that is missing data just like your case. I found when I clicked on the section of road it was divided into like 15 sections on this entrance alone. They don't give you the speed limit info on the website so it's hard to know exactly what's even going on. They do have speed limits on the mobile app but only when driving at the location. I don't think they have fixed the one I sent in the bug report on yet. It's definitely sub-optimal.


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## Misanthropic Mike (May 17, 2019)

Bear in mind that there is really no legitimate reason for TACC to initate uncommanded speed changes. As far as I'm aware, CC doesn't do this in any other vehicles.


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## M3OC Rules (Nov 18, 2016)

Misanthropic Mike said:


> Bear in mind that there is really no legitimate reason for TACC to initate uncommanded speed changes. As far as I'm aware, CC doesn't do this in any other vehicles.


They don't allow you to use autopilot more than 5 mph over the speed limit on city streets, etc. So when you transition to a road that is restricted it changes speed if it's more than 5mph over. This could be desirable if the map data was correct and will be required with FSD. TACC alone doesn't have the same restriction and I don't think it changes speed. Does it?


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## Long Ranger (Jun 1, 2018)

M3OC Rules said:


> TACC alone doesn't have the same restriction and I don't think it changes speed. Does it?


TACC alone doesn't change speed due to speed limit changes, but it will change speed temporarily if it determines that you are on a highway interchange or offramp. See my earlier post in this thread.


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## jsmay311 (Oct 2, 2017)

M3OC Rules said:


> They don't allow you to use autopilot more than 5 mph over the speed limit on city streets, etc. So when you transition to a road that is restricted it changes speed if it's more than 5mph over. This could be desirable if the map data was correct and will be required with FSD. TACC alone doesn't have the same restriction and I don't think it changes speed. Does it?


In the example I posted about earlier, it did change the set speed while using TACC.


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## M3OC Rules (Nov 18, 2016)

Long Ranger said:


> In your TMC post you say it happens at a freeway interchange. TACC can temporarily reduce your set speed at interchanges even if the speed limit doesn't change. From the manual:
> 
> When enabled while on a highway interchange or off-ramp, Traffic-Aware Cruise Control may reduce your set speed in 5 mph (5 km/h) increments - to as slow as 25 mph (40 km/h) - to better match the reported speeds of other Tesla vehicles that have driven at that specific location. To override this and continue cruising at your set speed, tap the accelerator pedal or touch the plus (+) or minus (-) button on the touchscreen. The new set speed is maintained for the duration of the interchange or off-ramp (unless you override it or cancel Traffic-Aware Cruise Control). After the interchange or off-ramp, the set speed may revert or change as necessary based on the new location. For example, if you merged onto a different highway, the set speed reverts back to the set speed that was in use before driving on the interchange.


It's interesting they have their own speed database. You'd think they could solve some of this missing map data with that. All I know is something needs to change or you're going to have self-driving cars going 30mph in areas where everyone else is going 60mph. That's unsafe and would make the passengers anxious to no end.


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## Misanthropic Mike (May 17, 2019)

Let's not even get into the brand damage that is assuredly going on with Tesla cars constantly slamming on their brakes on busy freeways and causing dangerous traffic interruptions. People are going to be saying "I wouldn't be caught dead in one of those things". They need to fix this yesterday.


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## Misanthropic Mike (May 17, 2019)

M3OC Rules said:


> They don't allow you to use autopilot more than 5 mph over the speed limit on city streets, etc. So when you transition to a road that is restricted it changes speed if it's more than 5mph over. This could be desirable if the map data was correct and will be required with FSD. TACC alone doesn't have the same restriction and I don't think it changes speed. Does it?


It does do this on TACC alone, and it does it on the freeway, and it will often suddenly change the speed to 30 mph below the speed limit. It does it at seemingly arbitrary and random points along the road, apparently in response to recent or historical traffic jams. It isn't just in my area either, I took a trip down to Brooklyn over the weekend and it happened in CT, NY, MA, and NH. These aren't obscure roads either, this is out on I95, the east coast version of I5 for you California users.


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## Mike (Apr 4, 2016)

Misanthropic Mike said:


> First off, I really wish Tesla would offer just ordinary cruise control so that I don't have to continually monitor my speed while cruising on the highway, because the "active" cruise is unusable in it's current form. It randomly changes it's setpoint while I'm cruising on the freeway, making my car suddenly decelerate for no reason. It's not only annoying, it's dangerous. Today on the way to work it just suddenly changed from a setpoint of 73 mph to 30 and began braking hard. This happened in broad daylight and good weather when there were no other cars for several hundred yards in front of me (not that it'd be OK for it to do this in any conditions). As a separate issue, it will frequently (like perhaps once or twice per mile) slam on the brakes while I am overtaking other vehicles in adjacent lanes, presumably because the software thinks the adjacent cars might be moving into my lane (they aren't).
> 
> As it stands, I really can't use cruise control at all without being seriously annoyed (and no doubt annoying the other cars around me), meaning my 2019 tesla has less automation than my 1989 honda accord had. I'm praying this is mostly due to my firmware version (2019.7.105) and the relative newness of HW3.


I find manually passing slower traffic on my right will often cause a momentary speed drop if using NOA or plain TACC.

The target is always at my front right quadrant.


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## SalisburySam (Jun 6, 2018)

Misanthropic Mike said:


> Bear in mind that there is really no legitimate reason for TACC to initate uncommanded speed changes.


Yeah, there actually is, and my car on 16.2 does this very, very well. Example: driving North on I-85 to Piedmont Triad International (PTI) airport. Using TACC, NoAP, and everything else. On its own with confirmation from me by torquing the steering wheel, the vehicle automatically exits I-85 (70mph limit), reduces speed for the ramp, resets speed for the next Interstate (65mph), automatically exits to another Interstate and resets speed to 55mph, the limit on that road, then takes exit to the airport ramp, again decreasing speed to the new 45mph limit. Then NoAP disconnects leaving TACC and AutoSteer going. Pretty amazing to me as it all worked well and without moments of terror for me or surrounding drivers.

To recap, this was four uncommanded speed changes, all of which were necessary due to either safety (reducing ramp speed) or changes in legal speed limits. In my opinion, the car needs to handle this, and it does.


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## Kimmo57 (Apr 10, 2019)

SalisburySam said:


> Yeah, there actually is, and my car on 16.2 does this very, very well. Example: driving North on I-85 to Piedmont Triad International (PTI) airport. Using TACC, NoAP, and everything else. On its own with confirmation from me by torquing the steering wheel, the vehicle automatically exits I-85 (70mph limit), reduces speed for the ramp, resets speed for the next Interstate (65mph), automatically exits to another Interstate and resets speed to 55mph, the limit on that road, then takes exit to the airport ramp, again decreasing speed to the new 45mph limit. Then NoAP disconnects leaving TACC and AutoSteer going. Pretty amazing to me as it all worked well and without moments of terror for me or surrounding drivers.
> 
> To recap, this was four uncommanded speed changes, all of which were necessary due to either safety (reducing ramp speed) or changes in legal speed limits. In my opinion, the car needs to handle this, and it does.


Nice if it works. On my way to work the street has a 60 km/h speed limit, but the car thinks it's 80 and wants to speed up, so that's not so great. There should absolutely be a setting to turn it off.


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## M3OC Rules (Nov 18, 2016)

Misanthropic Mike said:


> It does do this on TACC alone, and it does it on the freeway, and it will often suddenly change the speed to 30 mph below the speed limit.


It seems like that must be a map issue and it thinks its an exit ramp. I don't think I've seen this but I'm usually on AutoSteer. I verified today that on TACC alone and TACC+Autosteer do not always act the same. There is one section that I drive that on my commute that is a long entrance ramp. It switches from 55mph to 30mph and then back to 55mph on one section. If I have autosteer on it will lower the speed but if I have TACC only it will not lower the speed through this section. It kind of suggests multiple different types of map errors causing different behaviors on TACC only.


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## Mike (Apr 4, 2016)

Kimmo57 said:


> Nice if it works. On my way to work the street has a 60 km/h speed limit, but the car thinks it's 80 and wants to speed up, so that's not so great. There should absolutely be a setting to turn it off.


I went thru this same crap a year ago, over the first week I owned my TM3.

My ad hoc fix that seems to be the 90% solution is to set "relative" to "minus 30 (kph)" and use "relative".

See this link for more details: https://teslaownersonline.com/threads/learning-curve-speed-assist-and-default-settings.7158/


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## pdp1 (Nov 8, 2018)

I noticed the following happen at least twice since I updated to 16.2 (see picture below). I'm the green car and I have TACC on with the distance between cars set to 3. The red car in front of me decides to change to the lane to the right, cutting off the blue car. The blue car brakes because of the red car, but it causes my car to suddenly brake as well, which makes no sense to me because I wouldn't have slammed on the brakes in that case. The only far fetched explanation I can think of is that TACC now thinks the red car and blue car are the same car and is using the blue car as rear of the red car to judge distance? Regardless, it has been really annoying.


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## DocScott (Mar 6, 2019)

pdp1 said:


> I noticed the following happen at least twice since I updated to 16.2 (see picture below). I'm the green car and I have TACC on with the distance between cars set to 3. The red car in front of me decides to change to the lane to the right, cutting off the blue car. The blue car brakes because of the red car, but it causes my car to suddenly brake as well, which makes no sense to me because I wouldn't have slammed on the brakes in that case. The only far fetched explanation I can think of is that TACC now thinks the red car and blue car are the same car and is using the blue car as rear of the red car to judge distance? Regardless, it has been really annoying.
> View attachment 26580


Maybe it's over-correcting for another issue that has long been, at a minimum, unnerving.

Say it's a three-lane highway with a speed limit of 65 mph and the right lane is bumper-to-bumper, moving at maybe 10 mph stop-and-go. This may be because there's an exit that's backed up, or perhaps a stalled car or the lane closes up ahead. But the middle lane is clear.

Most humans driving in the middle lane will use a little caution, and drive somewhat below the speed limit--maybe 50 mph--just in case someone decides to jump out of the bumper-to-bumper lane. But AP has had a tendency to just assume that the people in the right lane won't be idiots and try to pull out when someone's coming. It's unnerving to have AP charging along at 67 mph (if I'm set at +2) right next to all those cars at 10 mph. In those situations I usually disengage and slow down a bit.

But in more recent updates, I notice AP has sometimes started to become aware of that kind of issue and may drive a little more cautiously in that situation.

The situation you describe may be making AP worried that someone might do something in response to the slowing in the right lane to bring them back in to yours--perhaps the blue car will try to get in to your lane to get around the red one.

A human is smart enough to understand the difference between the situation you describe and, say, a giant pothole in the lane that causes the blue car to brake and then maybe swerve around in to your lane, but AP isn't quite trained well enough to get that distinction yet, and so it slows down out of an abundance of caution.

Just a guess...


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## pdp1 (Nov 8, 2018)

DocScott said:


> Maybe it's over-correcting for another issue that has long been, at a minimum, unnerving.
> 
> Say it's a three-lane highway with a speed limit of 65 mph and the right lane is bumper-to-bumper, moving at maybe 10 mph stop-and-go. This may be because there's an exit that's backed up, or perhaps a stalled car or the lane closes up ahead. But the middle lane is clear.
> 
> ...


You might be onto something there. About 2 hours after my previous post, I was driving home and using Autopilot (I should have said Autopilot in my previous post, not TACC) on the freeway in the right lane, approaching a merge from an on-ramp lane. AP noticed a car approaching down the on-ramp lane, accelerating reasonably fast. A few seconds before said car even started merging onto the freeway, AP had my car to slow down, which was probably the right thing to do. So it seems AP was treating what I described in my previous post the same way as the situation I described in this post. I can see why to an AI both situations would be similar, but a human could tell the difference immediately.


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## Kimmo57 (Apr 10, 2019)

Mike said:


> I went thru this same crap a year ago, over the first week I owned my TM3.
> 
> My ad hoc fix that seems to be the 90% solution is to set "relative" to "minus 30 (kph)" and use "relative".
> 
> See this link for more details: https://teslaownersonline.com/threads/learning-curve-speed-assist-and-default-settings.7158/


Thank you, that's very helpful. Hopefully I can set it to -40 km/h, since I noticed yesterday, that the car suggested 80 km/h on a little 40 km/h street close to my home  That's 50 mph on a 25 mph street for those using the weird units.
Then if we could just find a solution to the unnecessary braking...


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## bwilson4web (Mar 4, 2019)

I verified the GPS map vs location problem tonight.

Entered zone at 50 mph and soon dropped to 40 mph:

















In 40 mph zone, it soon goes back to 50 mph:

















Here I combined a Google map image with icons showing what happens:








If your duration is short enough, the car in the left lane does not reset the TACC speed. In contrast, a larger zone in the right lane leads to a consistent drop to 40 mph.

Speculation, I suspect the different software releases may have different durations in a zone before the car begins changing speed. It would be great if there were some way to indicate a brief speed zone change for the humans.

Bob Wilson


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## SalisburySam (Jun 6, 2018)

Great. So when will T fix this annoyance?


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## bwilson4web (Mar 4, 2019)

SalisburySam said:


> Great. So when will T fix this annoyance?


My BMW i3-REx has 'mobileye' and reads speed signs. When Tesla implements reading speed limit signs, most of these will go away to be replaced with mobileye problems like school zone speed signs when school is out.

In the meanwhile, several suggestions for Tesla:

notification of a GPS-Google_Map speed reduction so the driver can understand and respond faster
specific bug report for speed anomaly so Tesla can fix map
resume original speed after short duration in new zone
stay with lead traffic if available
'remember' driver corrected speeds

provide an optional, map-independent, cruise control (i.e., old style)
I have another problem with TACC in the neighborhood. If I enable TACC headed south-east-south out, it sets the speed to 45 mph, not the 25-30 mph for a neighborhood. I know about it and *EVERY TIME* quickly dial it down. In contrast, going home, north-west-north, I can set the speed manually.

*LATE EDIT*: I got this in a Tesla e-mail:
​_Thank you for sending in the location and the video. This will very helpful for the autopilot team._​_I have sent it on to them for further research and a solution. While I cannot guarantee a time frame of when the issue will be fix, I can tell you they take all of our customers feedback very seriously in order to improve all Tesla vehicles. _​
Bob Wilson


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## bwilson4web (Mar 4, 2019)

I've posted a YouTube showing the video shared with Tesla. My dashcam was in 'time lapse' mode, ~2 frames/second, which in playback makes the action much faster. However, YouTube has both a playback speed control and the ability to stop and examine the video frame-by-frame.





Reproducible, I subsequently re-ran the left and right lane tests at 20 mph and could see the 'speed sign' icon change. It picks up the speed change but updating the speed sign icon takes longer. Meanwhile, the car drops from 50 mph to 40 mph in ~3 seconds.

*LATE EDIT:*
_I just checked the 'openstbreetmaps' view of the problem area and it shows only a single path mapped at 50 mph for both lanes. This suggests the Tesla GPS coordinates had wandered toward the 40 mph access road. _​
Bob Wilson


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## JustTheTip (Jun 7, 2018)

I was using TACC the other day. A car turned in front of me onto a side street waaaay ahead of me, and the car practically slammed on the breaks after the car completed its turn. I’m glad nobody was behind me. No doubt I would have been rear ended.


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