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Thoughts on why AEB is designed to only reduce speed by 25mph?

viet658

Member
Aug 11, 2013
134
56
Pomona, CA
B8DB286F-BFE7-4A36-AD17-F5ACF14BB47A.jpeg
Thoughts on why AEB is designed to only reduce speed by 25mph?
 

JeffK

Well-Known Member
Apr 27, 2016
6,997
6,657
Indianapolis
The primary goal is to begin the braking process and the human will take over thus mitigating the severity of the crash.

Brake too fast to a stop and someone will slam into you from behind. The keywords here are "When a frontal collision is considered unavoidable..."

If you've ever had a frontal collision, you'll know that, eventually, you do get to 0 mph.
 

S4WRXTTCS

Well-Known Member
May 3, 2015
5,631
6,406
Snohomish, WA
I think it's best explained with an example

Like lets say you're traveling down the freeway at 70mph, and there is a false detection with the AEB system. With a 25mph reduction it brings you down to 45mph. It's going to be unnerving, and you'll be irked. But, odds are no one is going to crash into you. Unless they're on your butt where they don't give the proper following distance.

If you went from 70 to 0 with as much braking power as the car could give you'd likely end up with some SUV on your back.

The 25mph was picked because that's enough of a reduction in speed to be life saving.

In the end it's just a way of managing imperfect technology.
 

viet658

Member
Aug 11, 2013
134
56
Pomona, CA
Thanks for the responses. I believe a lot of people probably didn't know this was part of the design and assume AEB would bring the car to a complete stop.
 

Devoldinho

New Member
Jul 19, 2017
4
12
Norway
I think it's best explained with an example

Like lets say you're traveling down the freeway at 70mph, and there is a false detection with the AEB system. With a 25mph reduction it brings you down to 45mph. It's going to be unnerving, and you'll be irked. But, odds are no one is going to crash into you. Unless they're on your butt where they don't give the proper following distance.

If you went from 70 to 0 with as much braking power as the car could give you'd likely end up with some SUV on your back.

The 25mph was picked because that's enough of a reduction in speed to be life saving.

In the end it's just a way of managing imperfect technology.

While this could be the reasoning from Tesla, does this mean that their technology is subpar compared to other car brands?

As always, I recomend everyone to check out Euro-NCAP’s reviews and videos were they test AEB as a part of the safety rating. AEB counts toward the rating, so it’s becoming quite common in Europe.

Here’s from the latest test of the Volvo XC60:

«The autonomous emergency braking system scored maximum points when tested at highway speeds, with collisions avoided at all test speeds and in all scenarios.»

Official Volvo XC60 safety rating

The Toyoya Prius also avoids the crash completly.

Official Toyota Prius 2016 safety rating

Had to do some digging to find a car that has AEB and does not avoid the crash in all scenarios, like Tesla:

Official Mazda CX-5 safety rating

The Mazda CX5 only reduces the severity of the crash if following a car at short distance and the car in front brakes harshly.

If being rear ended was a common occurance due to faulty AEB on other car brands, surely we would have heard about i more often?
 

Henry82

Member
Mar 25, 2018
91
52
Los Angeles, CA
Thanks for bringing this up... I was under the impression that AEB could bring the car to a complete stop... I doubt I'm alone in this misconception. TACC/EAP is fully capable of bring the car to a complete stop (and starting off again)... so the system is fully capable... I'm not understanding this -25 mph limitation.
 

JeffK

Well-Known Member
Apr 27, 2016
6,997
6,657
Indianapolis
While this could be the reasoning from Tesla, does this mean that their technology is subpar compared to other car brands?

As always, I recomend everyone to check out Euro-NCAP’s reviews and videos were they test AEB as a part of the safety rating. AEB counts toward the rating, so it’s becoming quite common in Europe.

Here’s from the latest test of the Volvo XC60:

«The autonomous emergency braking system scored maximum points when tested at highway speeds, with collisions avoided at all test speeds and in all scenarios.»

Official Volvo XC60 safety rating

The Toyoya Prius also avoids the crash completly.

Official Toyota Prius 2016 safety rating

Had to do some digging to find a car that has AEB and does not avoid the crash in all scenarios, like Tesla:

Official Mazda CX-5 safety rating

The Mazda CX5 only reduces the severity of the crash if following a car at short distance and the car in front brakes harshly.

If being rear ended was a common occurance due to faulty AEB on other car brands, surely we would have heard about i more often?
Let's take a closer look at the Volvo manual for details:
Adaptive Cruise Control utilizes approx. 40% of the vehicle's braking capacity. If a situation requires more braking force than the Adaptive Cruise Control can provide, and if the driver does not apply the brakes, a warning light and audible warning signal will be activated to alert the driver that immediate action is required.

Basically, if you're in stop and go traffic, it'll stop, just like a Tesla. If you're going highway speeds, then it will not necessarily stop the vehicle in time without driver intervention.
 

DR61

Member
Apr 14, 2016
561
619
Gold River, CA
«The autonomous emergency braking system scored maximum points when tested at highway speeds, with collisions avoided at all test speeds and in all scenarios.»

Official Volvo XC60 safety rating

I own a 2017 XC60 with this system. The manual says it only operates at 50 mph and below. For pedestrians and cyclists it suggests 30 mph and below. It does not say if it brakes to zero mph.
 

Matt_CRNA

Member
Jun 30, 2016
11
6
Oahu, Hawai'i
Definitely in place to reduce or mitigate front collision damage. Perhaps the AEB algorithm really only applies when Autosteer is off and a human has control of the vehicle?
 

brkaus

Well-Known Member
Jul 8, 2014
8,047
6,525
Austin, TX
I think it is simply the risk of being rear ended.

Some year, these systems will provide some sort of gap management... decide if it is worth running into the car in front to make more space for the car coming in fast from behind..

The automotive talk show guys on the radio in Dallas are always saying how AEB reduces injury BUT constantly harping on how manufactures don't explain that it will not come to a complete stop in many cases... They were not talking about Tesla, they were talking about AEB in general.
 
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ebmcs03

Active Member
Dec 22, 2017
2,186
1,132
So Cal
AEB designed to reduce the severity of the impact? So if it detects a crash and starts applying the brakes does that mean it’s too late and there’s going to be a crash no matter what? Like even if the driver takes over and steps on the brakes as hard as they can, is it too close to the object already and there’s not going to be enough braking distance?

Sounds like AEB reduces impact and cannot avoid it.
 

cizUK

Member
Mar 13, 2017
316
272
UK
I'm guessing that if there is a stationary car 5 metres away and you're going 25 mph less than you were 1 second ago, you're going to be pressing that brake pedal fairly hard;)
 
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JeffK

Well-Known Member
Apr 27, 2016
6,997
6,657
Indianapolis
AEB designed to reduce the severity of the impact? So if it detects a crash and starts applying the brakes does that mean it’s too late and there’s going to be a crash no matter what? Like even if the driver takes over and steps on the brakes as hard as they can, is it too close to the object already and there’s not going to be enough braking distance?

Sounds like AEB reduces impact and cannot avoid it.
Yes, that's exactly what it does. If the object you're going to crash into speeds away or if you're able to maneuver around it then you'll avoid the collision, but, for the most part, AEB should only go off if the collision is imminent.
 

BigD0g

Active Member
Jan 12, 2017
2,019
4,385
Somewhere
Because
1) false positives are dangerous
2) it's not an autonomous car

And just to add to this:

3) Liability.

If they go out saying it's going to 100% stop a car, and you smack into the back of someone, chances are you would hold Tesla liable. And given they can't even stop / move for fixed inanimate objects I would hold my breath for full stop AEB anytime soon.
 
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