# AEB When does it work?



## Drhalo (Jul 12, 2018)

I have a question about AEB. My friend was driving a Model 3, and was stopped at an on ramp to a highway. While looking over his shoulder to look at oncoming traffic during the merge, he accidentally rear ended a stopped car in front of him at under 15 MPH and caused 8K worth of damage to the tesla. 
He claims there were no audible warnings and no AEB. 
I am wondering under this scenario 1)Why AEB wouldn't work (this is a basic feature on many cheaper cars), 2)What scenario AEB can be trusted? 
We seem to hear about all the crashes with stationary objects, and I am wondering if there's a major deficiency in the video based crash avoidance system. It seems to have issues with stationary objects vs ones that are moving.


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## garsh (Apr 4, 2016)

AEB is designed to minimize an unavoidable impact. It's not guaranteed to eliminate impacts.

Here's the relevant excerpt from the Model 3 owner's manual:


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## Bigriver (Jan 26, 2018)

Drhalo said:


> ....on ramp to a highway. While looking over his shoulder to look at oncoming traffic during the merge, he accidentally rear ended a stopped car in front of him...


I've only had AEB activate for me one time, in a situation just like this, but it wasn't in a Tesla. Was in my Volvo XC40, and the car gave me both an audible warning and slammed on the brakes for me. No accident in my case. Disappointed that the Tesla didn't also avoid the accident. Low speed, it seems to me one of the easier ones the car should have been able to handle. My only thought is that if he had speed control activated but also had his foot on the accelerator, then the car states it will not do any emergency braking.


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## MelindaV (Apr 2, 2016)

it also is overridden by the driver having their foot on the accelerator.


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## MelindaV (Apr 2, 2016)

and another useful piece of info


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## FRC (Aug 4, 2018)

I've had precisely the same type of accident in a previous car. Never occurred to me to blame the car, I just thought I was an idiot.


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## Drhalo (Jul 12, 2018)

If you are going to hit another car, the aeb should stop the car or do everything it can to stop it. Seems to be a no brainer. Otherwise we are always going to mistrust it.


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## MelindaV (Apr 2, 2016)

Drhalo said:


> If you are going to hit another car, the aeb should stop the car or do everything it can to stop it. Seems to be a no brainer. Otherwise we are always going to mistrust it.


or just read the owners manual and understand it's limitataions


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## ravisorg (Jun 27, 2018)

So I understand why it didn’t apply brakes or stop the car in this situation, and that it’s operating within spec and according to the manual. So I’m not complaining that it didn’t brake and avoid the accident.

But I’ve been curious about this before, and maybe someone here knows. Why wouldn’t the car be programmed to prevent this? What technical or use case reasons, I wonder, would stop them from implementing a true “no I’m not going to allow you to drive into a solid object in front of the car” feature?

I understand it still wouldn’t be 100% if the car didn’t happen to detect something solid in front of it, but that doesn’t appear to be the issue here (or in other cars either).

I also understand that there are other cases where you wouldn’t want this to happen, like at high speed on the highway if there was a chance it was an errant reading. 

Anyone know?


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## Drhalo (Jul 12, 2018)

MelindaV said:


> or just read the owners manual and understand it's limitataions


You are completely missing the point.


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## garsh (Apr 4, 2016)

Drhalo said:


> You are completely missing the point.


No, it is _you_ who are completely missing the point.* AEB is NOT designed to avoid accidents.*

TACC is designed to avoid accidents via applying brakes.
Autosteer is designed to avoid accidents via applying brakes.
When it becomes available, FSD will avoid accidents via applying the brakes.

This is NOT what AEB is designed to do. *The only goal of AEB is to reduce the likelihood of injury when the car determines that an accident is unavoidable. * Given that your friend was not injured, it worked exactly as intended.


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## garsh (Apr 4, 2016)

ravisorg said:


> But I've been curious about this before, and maybe someone here knows. Why wouldn't the car be programmed to prevent this? What technical or use case reasons, I wonder, would stop them from implementing a true "no I'm not going to allow you to drive into a solid object in front of the car" feature?


The car is programmed to prevent accidents, but you have to specifically activate one of the driving modes to turn on this ability. Those are, namely, TACC and Autosteer. Currently, those are only usable in limited situations, so you couldn't (or at least, shouldn't) have them activated in the situation described in the original post.

As for why the car doesn't do this by default, that's because of "false positives". There's an entire thread about the phantom braking issues that people are seeing while using TACC and Autosteer. The car sometimes slams on the brakes for no good reason. At least I know that this will not happen unless either of TACC or Autosteer is activated. It would really suck if this happened all the time while driving the car. Those features (TACC and Autosteer) are considered BETA, so we begrudgingly accept that it happens, but I would be less willing to ignore that big deficiency if it were to happen just while driving the car myself.


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## atnbirdie (Jun 15, 2019)

The system is also designed to ensure the operator can easily over ride it if it makes a mistake. So if you have your foot on the accelerator it assumes you are taking over and will not brake. E.g., when on TACC if your foot puts any pressure on the accelerator a message pops up to tell you AEB will not work. At this point, the ability to over ride the system is a very good thing.


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## Drhalo (Jul 12, 2018)

At low speed if it senses you will hit something it should prevent it.
It's supposed to be more reliable than human operators right? According to Lord Elon. My buddy's Audi stopped Prevented this exact scenario.

I'm not arguing what's in the manual so the folks who want to recite Bible and verse can save the time. I'm just saying the system should be smart enough to prevent these things. 
If the sensors and system is smart enough in simple situations it should know when the operator is doing something stupid and override us mere mortals .

The whole highway speed thing and phantom braking, that is potentially where lidar could help and dare I say Elon might be wrong?


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## garsh (Apr 4, 2016)

Drhalo said:


> At low speed if it senses you will hit something it should prevent it.


You can say that all you want, but that's NOT what AEB is designed to do.


Drhalo said:


> It's supposed to be more reliable than human operators right? According to Lord Elon.


First, that is Elon describing Autopilot mode. In particular, Autosteer. Which as I stated above, _is_ designed to prevent collisions.

Second, he has never said that it's more _reliable_. He says that - statistically speaking - it is _safer_ than a human driver. That's a very different thing. A Tesla on Autopilot has fewer accidents per mile driven than a human. But it does have accidents. It does make mistakes.


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## Patrickt888 (Aug 6, 2019)

Interesting how Tesla's AEB is different than some of the ICE car. My 2017 RX350 did a complete stop on both occasions. One when someone took a left turn in front of the car at a 4 way stop, and One while backing out of a packing lot


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## Bigriver (Jan 26, 2018)

Wow, much stronger statements and opinions on this than I would have thought.

It seems that the main points are:

that Tesla's AEB is not designed to prevent accidents but only to mitigate the consequences of accidents,
that a hard acceleration will prevent or cancel AEB,
that AEB would not be actuated if under 7 mph,
that a user could have AEB turned off in the settings,
that a driver is ultimately responsible for their actions and inactions.
Although I do not sit back and rely on the AEB, it is something that I have thought is important. It is a feature that exists on every Tesla, whether or not the car has autopilot. The scenario presented in the OP seems worthwhile to consider (on-ramp's are awful where I live) and I do not easily rest in the car-worked-as-it-should camp. No one was hurt, but it was a low speed accident with relatively high cost damage. The information we have is second-hand and may not be complete, but if he was going over 7 mph and moving forward without a hard acceleration, I think the car should have helped cover his goof. Specifically some of the concerns I still have are:

Shouldn't there have been an audible warning from the Forward Collision Warning system, which is to precede the application of AEB?
What about the obstacle-aware acceleration, which is to limit your acceleration if an obstacle is detected in front of you at low speeds.... is a vehicle in front of you an obstacle?
Purchasing a Tesla does not make me a part of the design team, so I understand that I have to deal with however it is designed (which I love most things about it). But we should still feel free to voice concerns.... and other car manufacturers (Volvo and Audi have been mentioned) do prevent a collision in this specific scenario. It's not outlandish to hope that Tesla would too.
I can know my car and read the user manual often (which I do), but none of us fully know how the car will respond in emergency situations unless we experience it, or get to learn from other's experiences. Thus the value of this forum.


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## NR4P (Jul 14, 2018)

I have had the Forward Collision Warning System make noises a few times. 
TACC or EAP is not in use 

Example. I am doing 60 mph on a 4 lane divided road A truck turns across my lane. Car squels with warning. I am prepared to brake or veer into other lane if truck doesnt clear my lane fast enough. 

Not once have the brakes been applied automatically. 

What am I missing?
EAB is on.


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## slasher016 (Sep 12, 2017)

I drive fairly aggressively in general and my forward collision warning system goes off all the time. It's saved me a few times. It makes a loud noise and the car you're about to hit turns red. Maybe you need to adjust the settings on your forward collision warning?


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## NR4P (Jul 14, 2018)

slasher016 said:


> I drive fairly aggressively in general and my forward collision warning system goes off all the time. It's saved me a few times. It makes a loud noise and the car you're about to hit turns red. Maybe you need to adjust the settings on your forward collision warning?


 The warning is fine.

But no braking ever applied except phantom braking.

Seems like others are questioning this too.


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## garsh (Apr 4, 2016)

Guide to Automatic Emergency Braking
Consumer Reports, so it's probably paywalled.
False alarms in these systems are horribly annoying.


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## garsh (Apr 4, 2016)

No automaker's AEB system is guaranteed to prevent collisions.
Car & Driver performed testing of AEB systems on four cars.

We Crash Four Cars Repeatedly to Test the Latest Automatic Braking Safety Systems

The car companies don't hide the fact that today's AEB systems have blind spots. It's all there in the owner's manuals, typically covered by both an all-encompassing legal disclaimer and explicit examples of why the systems might fail to intervene. For instance, the Camry's AEB system may not work when you're driving on a hill. It might not spot vehicles with high ground clearance or those with low rear ends. It may not work if a wiper blade blocks the camera. Toyota says the system could also fail if the vehicle is wobbling, whatever that means. It may not function when the sun shines directly on the vehicle ahead or into the camera mounted near the rearview mirror.​​There's truth in these legal warnings. AEB isn't intended to address low-visibility conditions or a car that suddenly swerves into your path. These systems do their best work preventing the kind of crashes that are easily avoided by an attentive driver.​​The edge cases cover the gamut from common to complex. Volvo's owner's manuals outline a target-switching problem for adaptive cruise control (ACC), the convenience feature that relies on the same sensors as AEB. In these scenarios, a vehicle just ahead of the Volvo takes an exit or makes a lane change to reveal a stationary vehicle in the Volvo's path. If traveling above 20 mph, the Volvo will not decelerate, according to its maker. We replicated that scenario for AEB testing, with a lead vehicle making a late lane change as it closed in on the parked balloon car. No car in our test could avoid a collision beyond 30 mph, and as we neared that upper limit, the Tesla and the Subaru provided no warning or braking.​​At the moment, automakers have few incentives to push AEB performance beyond the tests already used in regulatory assessment programs and safety ratings. NHTSA's stationary-vehicle AEB test is performed at a single speed, 25 mph, and it only requires that the vehicle scrub off 9.8 mph before impact.​


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## shareef777 (Mar 10, 2019)

garsh said:


> The car is programmed to prevent accidents, but you have to specifically activate one of the driving modes to turn on this ability. Those are, namely, TACC and Autosteer. Currently, those are only usable in limited situations, so you couldn't (or at least, shouldn't) have them activated in the situation described in the original post.
> 
> As for why the car doesn't do this by default, that's because of "false positives". There's an entire thread about the phantom braking issues that people are seeing while using TACC and Autosteer. The car sometimes slams on the brakes for no good reason. At least I know that this will not happen unless either of TACC or Autosteer is activated. It would really suck if this happened all the time while driving the car. Those features are considered BETA, so we begrudgingly accept that it happens, but I would be less willing to ignore that big deficiency if it were to happen just while driving the car myself.


This! With TACC/AP you're expected to maintain extra vigilance behind the wheel. If AEB could activate anytime phantom braking would likely cause more accidents then prevent.


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## M3OC Rules (Nov 18, 2016)

Maybe the way to think about this is there is absolutely no situation where you rely on AEB. So it doesn't really matter if you know when it works or doesn't because you shouldn't change how you drive whether you have it or not and there is no training required. Now if you're buying a car you may want to know how well it works for reducing accidents and phantom braking so its a fair question. The IIHS certainly wants to know how well these systems work since they will change how it costs to insure them. They test AEB at 12mph and 25mph approaching a fake stationary car and say the Model 3 avoided a collision. I assume that means it stopped?

They say "For a superior rating, a vehicle must have an autobrake system that can avoid a crash or substantially reduce speeds in both tests."


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## Bokonon (Apr 13, 2017)

I wish Tesla would make a video demonstrating exactly what AEB does and does not do, and contrast it with the forward collision warning. I get that it would tricky from a messaging perspective ("wait, my car will warn me about an potential crash, but not do anything about it?"), but there seems to be a persistent lack of clarity among some owners about what these features actually do, and when they are active. A visual aid we could share might help clear things up.


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## JWardell (May 9, 2016)

As usual, Tesla hasn't done quite a good enough job communicating the details of its many features, and confusion and upset posting results.

While I agree, it would be VERY NICE for these cars to prevent a driver from ever hitting anything, that feature does NOT exist. It only does this when the car is driving itself in AP or TACC and the driver is not touching the pedals. The car ALWAYS gives the driver priority over the system when they operate the controls. Again, it would be nice in many instances for the car to ignore your commands to prevent what it things is touching anything, but what most don't think about is the annoyance and possible serious issues that exist when the computer mistakenly thinks there is an object and suddenly you are not allowed to drive. I don't think we will see this feature until full self driving is 99.9999% perfect which is very far off.

(Yes, I would like an option to enable something like this, and a button to override to say "Yes please let me drive into this"...)

Till then people are going to continue having fender benders and drive though storefronts, and it will continue to be their own fault.


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## M3OC Rules (Nov 18, 2016)

Bokonon said:


> I wish Tesla would make a video demonstrating exactly what AEB does and does not do, and contrast it with the forward collision warning. I get that it would tricky from a messaging perspective ("wait, my car will warn me about an potential crash, but not do anything about it?"), but there seems to be a persistent lack of clarity among some owners about what these features actually do, and when they are active. A visual aid we could share might help clear things up.


Go watch Youtube videos of Tesla's crashing into things. That's all you need to know. If you want to see it work you can watch IIHS test videos. But that's my point is that you can't rely on it so you still need to pay attention and try not to run into anything. Its like stability control. It can help save someone from getting out of control but it's not perfect. You don't know where the limit is but it doesn't matter.

Edit: Just to clarify this is from the drivers perspective and why Tesla or the driver probably doesn't benefit from a video like this. How well it works does matter from a safety perspective and a user experience perspective(phantom braking). Tesla does provide statistics on crashes versus other cars albeit without a lot of detail to tease out something like AEB performance.

Edit 2: Here is a video from Nissan. And another one from Kia. The Kia one shows you how to turn it off but doesn't explain why you might want to do that. I think these videos probably do more harm than good despite their disclaimers.

Edit 3: Here is a couple of videos Tesla shared. These are not great since they are from the cars front camera. This basically is an advertisement not unlike the Nissan and Kia ones. Maybe one good aspect of this is everyone should have this tech on their car and advertising will help that. It just gets tricky if you mislead people on how well it works.


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## Mistersandman (Sep 23, 2017)

I had AEB activate on me today. I was driving in stop and go traffic when the car in front of me accelerated and stopped abruptly. I accelerated as well and had to firmly apply the brakes shortly thereafter to avoid hitting him. I didn’t apply the brakes very hard, (maybe 75%?) since I had good control of the cars deceleration and would have stopped about 2 feet away from his rear bumper. I guess this was too close for the car so it decided to apply the AEB for me. What’s crazy is that it slammed on the brakes so hard that I thought I was rear ended from behind. Did it prevent me from hitting the car in front? I don’t think so. However, if I was not good at gauging the distance I could have easily hit the car in front of me. So for anyone that hasn’t felt it before, be warned that it is a pretty good jolt.


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