Hi and sorry if this was posted before. Have anyone experienced this? I will be on a highway on autopilot at the speed of 70 where the speed limit is 65. Then suddenly the car would decrease the speed to 55! I have been paying close attention and it seems to happen at the same spot where for approximately 100 yards the speed limit symbol disappears from the screen. It’s almost like if it doesn’t know the limit at that particular section of the highway it will default to 55? I’ve had many close calls where I had to take over and slam on the accelerator to keep the car following me from rear ending “my precious.” Is there a thread about this? Is it a bug? Seems it should just rely on following the car in front rather than slowing the car down like this.
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Autopilot dangerously reducing speed on highways
- Thread starter LoveMyM3
- Start date
LowBattery
Member
As Fresnel said, it is fairly common. I generally only turn on autosteer if the drivers behind me have been maintaining a healthy distance.
Knightshade
Well-Known Member
That's not phantom braking at all. Phantom means it'd doing it without any obvious reason... (a phenomenon I've yet to experience in over 15,000 miles of driving, mostly on autopilot)
The thing you describe isn't phantom braking- lane-adjacent speed reduction was added intentionally in a recent update.
The OPs case isn't either- there IS an obvious reason in the OPs case- the car no longer thinks it's in a 65 mph zone because the maps are wrong.
So long as Tesla relies on map data for speed limits, and that data isn't perfect, this is going to happen.
Relying on the car in front of you to pick a max speed (other than TACC insuring you don't hit the guy) makes no sense because if the guy in front of you is a maniac who wants to drive 30 over the limit you probably don't want YOUR car doing that do you?
HyperionMark
Member
I think this is different than phantom braking. This is where it doesn't know the speed limit, therefore 45 or 55 is the top autopilot speed slowing the car down dangerously. I've had it happen a fair amount on this version. Will likely go away with the next one.
Whatever it's called, it's disturbing, potentially dangerous, and shouldn't occur
One of the many.. this is why we remember to always pay attention and don't pet dogs in the back seat while using AP/NOA
Knightshade
Well-Known Member
On a divided limited access highway with a known speed limit- it is.
The OP notes his speed limit on the display vanished- at which point AP usually reduces max speed- the owners manual points this out in the AP section.
This isn't an AP bug- AP is working exactly as intended.
It's a map problem.
I really disagree with this definition. In the vernacular of the community as I understand it, phantom braking is braking done without a need regardless of the obvious reason. The most common one being braking while adjacent to a large truck regardless of if the truck is actually moving into your lane.
It would be less dangerous if the slowdown was more gradual rather than abrupt enough to create the risk of getting rear ended.
I agree with @Knightshade, we drive on Hwy 290 in Houston where it had been under major renovation for about 7 years. It's pretty much done, about 3 years behind schedule, the two biggest issue I have with the renovation is 1) striping is not complete and 2) speeds are not updated for Tesla usage. The speed signs appear to be correct but the database that Tesla uses is not. Same portion of the hwy will go from 65mph to 45mph. 45 was the construction speed years ago, it is annoying and dangerous.
Has there been construction there within the last 6 months to a year? There is a stretch of highway near me that had construction and a temporarily reduced speed limit and for the last 6 months (since the construction ended) my car slows down there from 60mph to 50mph. I don't know that the prior construction is the reason it does it, but it's the only reason I can think of.
This happened to me as well few times on high way. No matter what we call it (Phantom braking or what so ever..) but I really feel it is dangerous and the passenger was really felt like the car hit somebody in the front. It is really that slow all of sudden.
Just wondering if this can be fixed with any of the available AP settings in the car without waiting for next software update. Any thoughts?
Knightshade
Well-Known Member
No.
There's nothing to "fix" with AP.
AP is working exactly as intended
The problem is the map has the wrong speed limit (or in this case, apparently NO speed limit since he said the sign vanished rather than just became a lower speed)
I think a lot of folks in this thread would benefit by reading page 85 of the current Model 3 Owners manual that explains how AP speed restrictions work.
Basing it only on map data is a bad way to do it in this always changing world it's never.. ever going to be fully accurate so that problem will never go away.
That is totally understandable. Two things here that can avoid this dangerous situation:
1. Let the car move with the speed that was set to in AP (65, 70 mph etc..) without interfering with posted speed and this should be controlled by the driver not posted speed in maps
2. There should be a setting in AP that can give us options a) you want to follow the speed as per maps b) manually control the speed in AP.
1. Let the car move with the speed that was set to in AP (65, 70 mph etc..) without interfering with posted speed and this should be controlled by the driver not posted speed in maps
2. There should be a setting in AP that can give us options a) you want to follow the speed as per maps b) manually control the speed in AP.
I'm sure they've known about this problem for a very long time (over reliance on maps), we just have no visibility to how they are planning to address it. There really isn't much of a financial incentive for them to devote resources to fixing it in the near future. They are likely focusing on features that can be released as FSD revenue. The whole business model is based on pushing out partially working software (typical of a tech company).
A lot of "buggy" (even though it's not a TACC bug, more like an overall flaw in the driver assistance system) features generates more revenue than chasing down all the problematic parts of existing feature sets.
We're all waiting for the pot of gold at the end of the HW3 rainbow.
A lot of "buggy" (even though it's not a TACC bug, more like an overall flaw in the driver assistance system) features generates more revenue than chasing down all the problematic parts of existing feature sets.
We're all waiting for the pot of gold at the end of the HW3 rainbow.
yes and there should also be a feature to completely turn off TACC and run dumb cruise control sometimes for especially problematic situations like this.
they could also put in an "anti brake-check" algorithm to the automatic speed change subsystem that would cap the amount of braking force/deceleration based on the distance of the car behind. This is called "anti-jerk" logic in conventional ICE vehicles, often used to cap jarring behavior on acceleration.
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