2020 FSD - Phantom braking - navigate on AP.

[outdoordawg]

It scared the bejesus out of me!!! Took delivery of my M3 with FSD yesterday, and took a long drive to lunch this afternoon, I was cruising down the freeway on FSD at 65mph and there it was .. it slammed on the breaks for no apparent reason! There was a large semi few cars behind me.. had he been any closer I don't think he would have the time to slowdown on time. I have read people talking about this "phantom breaking" and having experienced one today, I now know how scary it is. How often does this happen? is it a once a while glitch or is it too frequent for me to worry about?

 

[Ryephile]

It happens most often on high-contrast (sunny) days when you drive under an over-pass. Best driving practice to avoid being rear-ended from it is to hover your foot over the accelerator pedal to quickly take over control.

 

[Puddles]

Rye is right. It was weird to realize that instead of covering the brake, I had developed the habit of covering the accelerator. That was a year ago, and I still find it's a good idea. This has been a long-term issue. It must be hard to solve.

But we digress! You got your new car! Congrats!

There is definitely a settling-in period as the way the car drives itself is (probably) much different than the way you would drive it. It will take time for you to feel comfortable letting it have its way.

 

[totteraptor]

For me it is frequent enough that my wife HATES when I drive with AP on... :-(

 

[67King]

Doesn't even require AP. Just plain cruise control will do it. I had the worst case happen to me yesterday. Was driving on a state highway, 2 lane, and an oncoming car, both of us well within our lanes, caused mine to not only hit the brakes, but hit the emergency stop feature, and starting sounding the beeping alarm warning me of an impending collision.

Personally, I wish I had just plain dumb driver aware cruise control, which I feel would be much safer than the overly reactionary AI based one.

Disclaimer: To avoid the lecture I typically get from one poster about only using the feature on access controlled, divided highway, the owner's manual states no such thing about TACC.

 

[Mickeyflea]

I've had a few instances of phantom braking when on AP and I think that may be linked to passing under a bridge or underpass.

Is this still happening to others?

Does anyone have any ideas/solutions for this?

Cheers all

 

[bcompton32]

This has happened to us several times. It is much worse than scary it is very dangerous. Someone is going to get rear ended with this bug if they haven’t already. Very ironic that there is such a dangerous bug from a company that counts safety as their top priority.

 

[Knightshade]

This has happened to us several times. It is much worse than scary it is very dangerous. Someone is going to get rear ended with this bug if they haven’t already

So first- it's not a bug.

All cars with radar cruise do this.

Other brands have had outright recalls because of how much worse they do it than Tesla.

Second- everyone has been saying for years how "dangerous" it is, yet nobody, for years, has ever provided any examples of someone getting rear-ended in a Tesla from it. Weird huh? In fact one member actually measured the behavior with an accelerometer and found the braking wasn't nearly as hard as it subjectively "seemed" to be either (not significantly different than just regen braking, FAR from ABS hard braking)


Not to mention If someone is following you so closely they can't slow down when you do, they are the one engaging in dangerous behavior, and most states explicitly have laws against following too closely for this reason and (in those states that assign blame in accidents) generally assign it to the guy behind you.

But again... the braking isn't usually nearly as severe as the person in the car thinks it is and it hasn't AFAIK to seen in years on here caused any accidents at all.

 

[67King]

It is a bug. A response to a misidentification is a bug. It may be common across vehicles, but it is a bug.

Very typically, the accident involves cars behind the vehicle that actually initiates the incident. THe phenomenon is known as the accordion affect. NHTA assumes 1.3 seconds for a reaction time. At 70MPH, that is 130 feet. So 130 feet of travel before a response, meaning the car behind teh brake checked one has to slow even harder. After a few subsequent cars, things "accordion" and an accident happens.

It is real, it causes problems, and it has been documented. For example: Tesla Model 3 Brake Checks Semi Truck on Autopilot: Video

 

[Knightshade]

It is a bug.

No, it's not. It's a fundamental consequence of radar cruise control.

Again- it's not specific to Tesla, all brands that use radar have it- many worse than Tesla does.

The system is behaving exactly correctly within the limitations of the hardware.


This link explains it pretty well-

Why Tesla's Autopilot Can't See a Stopped Firetruck

The same is true for any car currently equipped with adaptive cruise control, or automated emergency braking. It sounds like a glaring flaw, the kind of horrible mistake engineers race to eliminate. Nope. These systems are designed to ignore static obstacles because otherwise, they couldn't work at all.

It goes on to point out

You always have to make a balance between braking when it’s not really needed, and not braking when it is needed

So essentially on one end of radar cruise you have a system that brakes WAY WAY too often, almost unusably so... and on the other end you have a system that FAILS to brake WAY WAY too often, almost unusably so.

So you have to pick a balance point where the system is useful and as safe as possible within the limits of the tech.


That's why it's better, or worse, in some brands versus others- they pick difference balances- but in all of them is the same inherent limit of the technology.

It's not a bug- it's literally endemic to the tech of using radar for your cruise control.

The article goes on to explain:

The long term solution is to combine a several sensors, with different abilities, with more computing power.

In other words- the problem happens when you rely on radar. Eventually it can be mitigated with using additional things---the story specifically mentions LIDAR, but Tesla has decicided Vision will be sufficient eventually.

It also cites more computing power- whcih is what HW3 brings to the table.

It is real, it causes problems, and it has been documented. For example: Tesla Model 3 Brake Checks Semi Truck on Autopilot: Video

I notice no accident actually happened in your video- despite it being a semi that was following an unsafely close distance.

Surely if Teslas system was SUPER DANGEROUS you'd have lots of examples of actual accidents it caused... right?

Where are they?

 

[Marius A]

This has happened to us several times. It is much worse than scary it is very dangerous. Someone is going to get rear ended with this bug if they haven’t already. Very ironic that there is such a dangerous bug from a company that counts safety as their top priority.

The phantom braking makes for a horrifying driving experience, but I don't think it's as dangerous as people like to make it.
The car slams the brakes out of nowhere, and it feels extremely awful, but you've usually stepped on the accelerator again before a full second has passed.
The TM3 is, by leaps and bounds, much worse on this than the TMS. I can only make assumptions about why, so I'm not gonna bother.
The dangers about phantom braking as I see it is:
* People are driving too close on your tail so you will be involved in a crash
* The person behind you brakes in response, and somebody is tailing that person too closely (I witnessed this happening once, the TM3 sped off and the two other cars were left to deal with insurance. I was in car #4 and managed to brake in time)
* It makes other drivers anxious and try to overtake you and leave you (the cause) behind
* Someone in the car isn't strapped in properly and get hurt. I can't imagine it would be serious injury, though.

I just find it extremely awful, so I don't use it. If I use TACC I will turn off automatic emergency braking (which won't stay off).
Granted, I've only tried adaptive cruise in Tesla (TMS and TM3), Mercedes, VW, Mazda and Hyundai so I don't have the biggest comparison chart, but the phantom braking I've experienced in those aren't comparable to how awful the TM3 is.

 

[Iain]

Are some cars just better than others? I’ve had my car for 11K miles and have had one scary phantom braking. I’ve had several small ones and I use FSD 90% of the time. My wife who is a nervous passenger has never complained and prefers I use FSD on the freeway because it does such a good job.

 

[Knightshade]

Are some cars just better than others? I’ve had my car for 11K miles and have had one scary phantom braking. I’ve had several small ones and I use FSD 90% of the time. My wife who is a nervous passenger has never complained and prefers I use FSD on the freeway because it does such a good job.

Yeah I've got about 25k miles on mine, 90%+ on AP/NoA (virtually all on highways) and almost never have this issue either.... I've had a small handful of times (mostly my fault when on a local road) where it slowed 10-20 mph before resuming....but virtually never any kind of "scary hard" braking on a highway

One owner in a previous thread found setting emergency braking to early caused a LOT more incidents of it that went away when he changed the setting to late- which was then confirmed by other users who tested it... (which is where mine has been set the whole time) so it's possible that's the issue for some folks.

There also seems to be a geographic component (some places the maps are specifically labeled to ignore things that can cause phantom braking events like overpasses, but not all of them everywhere are so labeled and again this is the balance of safety versus usefulness as an explicit override isn't the safest idea either)

And lastly there's a user error component where people use it on roads the manual explicitly tells them not to (roads with 2 way traffic and sharp curves for example) and that's entirely the drivers fault.


The expectation is once Tesla has vision "solved" the issue vanishes because the cameras will understand enough to know if what the radar is telling it to stop for makes sense or not.

 

[Marius A]

Are some cars just better than others? I’ve had my car for 11K miles and have had one scary phantom braking. I’ve had several small ones and I use FSD 90% of the time. My wife who is a nervous passenger has never complained and prefers I use FSD on the freeway because it does such a good job.

It seems to vary, and how bad people think it is varies a lot as well.
I've had 2 TM3, one was hw2 and the other hw3. The first one was extremely bad, I stopped using cruise control altogether. The second was much better, but that sudden jerk just leaves me shaky so I preferred not to use it.
If you have the right environment to use NoAP you've probably got the better conditions.

Some people are such zealot defenders of Tesla that they try to pin it on "unsuitable road conditions" and stuff like that, but phantom braking happens just as much on TACC as AP/NoAP.
I think phantom braking is awful on the TM3, but it's not like there's a stockpile of dead people in a ditch because of it.
But we tend to speak in absolutes when we want to get our points across, which doesn't really promote constructive debate.

 

[Wingsy]

For me it is frequent enough that my wife HATES when I drive with AP on... :-(

Mine too!

Elon, help us!

 

[Wingsy]

No, it's not. It's a fundamental consequence of radar cruise control.

I beg to differ with you there. I had a 2011 Dodge Charger that I drove for 1 year, then a 2012 Charger I drove for 7 years. Both with adaptive cruise which I used all the time. And yes, it did brake and sound the collision alarm on rare occasions - and every time it was when rounding a curve and encountering a mailbox or similar metal object. It never ever did any unexplained braking or alarm when on the open road, like an expressway. I've been traveling down the interstate with nothing around me - no bridge, no semi, no nothing, and my M3 would panic brake. THAT's the phantom braking that I experience, and I definitely call it a bug.

 

[Knightshade]

I beg to differ with you there.

I mean, you can't though. What I stated is a factual description of the feature.

I had a 2011 Dodge Charger that I drove for 1 year, then a 2012 Charger I drove for 7 years. Both with adaptive cruise which I used all the time. And yes, it did brake and sound the collision alarm on rare occasions

Right. Because all radar systems have this same problem.

Weird you'd beg to differ and then point out I'm right.

- and every time it was when rounding a curve and encountering a mailbox or similar metal object. It never ever did any unexplained braking or alarm when on the open road, like an expressway. I've been traveling down the interstate with nothing around me - no bridge, no semi, no nothing, and my M3 would panic brake. THAT's the phantom braking that I experience, and I definitely call it a bug.

It's not though.

It's exactly the same issue

ALL radar cruise systems have this issue. It's inherent to the tech.

You have to pick settings that allow it to work at all (rather than brake for every stationary radar return on a guardrail or whatever) versus settings that cause it to slam into other cars 100% of the time (ignoring all stationary radar returns).

You have to pick what balance point you think offers the best performance versus safety.

Dodge picked a different balance point between function and safety than Tesla did...more toward performance than safety... Tesla is a touch further toward safety.

Both of which are both different from the one say Ford and Mazda and Nissan each picked (their picks were so bad they all had to issue recalls since lack of OTA updates made it impossible to correct otherwise and unlike Tesla was so bad it ACTUALLY caused crashes)


Because, again, ALL radar cruise systems have this issue. It's inherent to the tech.

The degree will vary, but that's not a bug it's an intentional choice by the programmers.

 

[Need]

I am pretty sure phantom braking has something to do with shadows or dark patches on the road. I drove about 40% at night and 60% at day. I use AP or TACC pretty much all the time and I never had phantom braking happened at night.

Also when it happens, you feel like the car is slamming on the brake like doing an emergency stop. But I think in reality, it is more like one of those drivers who like to tap the brake for no reason at all while driving on the freeway. I think because you did not control the braking and it came suddenly so you felt that it was much stronger than it was.

 

[67King]

I am pretty sure phantom braking has something to do with shadows or dark patches on the road. I drove about 40% at night and 60% at day. I use AP or TACC pretty much all the time and I never had phantom braking happened at night.

Also when it happens, you feel like the car is slamming on the brake like doing an emergency stop. But I think in reality, it is more like one of those drivers who like to tap the brake for no reason at all while driving on the freeway. I think because you did not control the braking and it came suddenly so you felt that it was much stronger than it was.

There are multiple causes. Shadows are one. I have noticed that the severity and frequency of it varies, often with software updates. I have experienced it in the dark, and used to daily. But the car has now figured it out (granted, I've already got 50,000 miles on it, so it has ample opportunity to learn). There is one of those long term construction zones I drive through often multiple times per day, starting with the pre-dawn hours. It is one of the ones where the work is done during certain hours, and the barrels are moved back and forth. My car used to brake check there, slowing down about 10MPH pretty much instantly, then coasting down another 10 (at a speed that the brake lights are engaged) and staying around there until I pressed the throttle. I believe the cause was one of the signs, as it was always the same place (which is nice, because if you are expecting it, simply pressing the throttle will override until you are past the point). I still get teh occasional unexpected shadow. And like I pointed out with the video above, it can be pretty sudden, enough to cause an accident behind you, that you will neither be involved in, nor potentially even see. Another issue is that it will do it if vehicles are crossing in front of you for any reason, even at several hundred feet, such as a divided highway.

 

[Knightshade]

There are multiple causes. Shadows are one. I have noticed that the severity and frequency of it varies, often with software updates. I have experienced it in the dark, and used to daily. But the car has now figured it out (granted, I've already got 50,000 miles on it, so it has ample opportunity to learn).

Individual cars do not learn.

All behavior is the same car to car (barring the basic user-controlled settings like early/normal/late for emergency braking), based on the firmware the car is running pushed out from Tesla.

There is one of those long term construction zones I drive through often multiple times per day, starting with the pre-dawn hours. It is one of the ones where the work is done during certain hours, and the barrels are moved back and forth. My car used to brake check there, slowing down about 10MPH pretty much instantly, then coasting down another 10 (at a speed that the brake lights are engaged) and staying around there until I pressed the throttle. I believe the cause was one of the signs, as it was always the same place (which is nice, because if you are expecting it, simply pressing the throttle will override until you are past the point). I still get teh occasional unexpected shadow. And like I pointed out with the video above, it can be pretty sudden, enough to cause an accident behind you, that you will neither be involved in, nor potentially even see. Another issue is that it will do it if vehicles are crossing in front of you for any reason, even at several hundred feet, such as a divided highway.

So...construction zones- which the owners manual specifically tells you not to use the system in... .and roads with cross-traffic- which the owners manual specifically tells you not to use the system in.

Also when it happens, you feel like the car is slamming on the brake like doing an emergency stop. But I think in reality, it is more like one of those drivers who like to tap the brake for no reason at all while driving on the freeway. I think because you did not control the braking and it came suddenly so you felt that it was much stronger than it was.

Yup. One owner in a previous thread actually measured with an accelerometer and the braking was only about 0.2g... pretty much the same as just regen braking. Humans are terrible measuring devices.