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Almost Rear Ended Due to Autopilot Hard Breaking?

Travelhead

Member
Aug 3, 2019
40
24
Fl
Driving with my parents yesterday with autopilot engaged going about 70 mph on the highway. Cars start to slow down, so autopilot adjust down to 50, 40mph, then the car in front of me comes to a smooth stop and my car has plenty of time to smooth stop, but INSTEAD autopilot goes full on HARD STOP (it seems autopilot breaks really hard), and the person behind me nearly rear ended me! I had to quickly accelerate to avoid getting hit from behind.

1) is there a way to adjust autopilot so it stops smoother instead of a hard stop which can cause rear ends like what l describe above?

2) does this happen to anyone else?
 

VT_EE

Active Member
Apr 22, 2017
2,077
2,777
Maryland
It does happen sometimes when the person in front of me hard brakes. Instead of using the space between my car the one in front to reduce the braking force involved, it just tries to keep the following distance the same. The result is an unnecessarily hard brake, which is bad if the the guy behind you is following too close.
 

cjlogan30

Member
Sep 4, 2019
7
5
Gurnee,IL
Autopilot hard breaking has been happening to me as well on my morning commute. Its been more prevalent since the latest update. Not sure why its doing that even when vehicles are no where close to me.
 

BZM3

Member
Aug 15, 2019
281
183
Somewhere
Driving with my parents yesterday with autopilot engaged going about 70 mph on the highway. Cars start to slow down, so autopilot adjust down to 50, 40mph, then the car in front of me comes to a smooth stop and my car has plenty of time to smooth stop, but INSTEAD autopilot goes full on HARD STOP (it seems autopilot breaks really hard), and the person behind me nearly rear ended me! I had to quickly accelerate to avoid getting hit from behind.

1) is there a way to adjust autopilot so it stops smoother instead of a hard stop which can cause rear ends like what l describe above?

2) does this happen to anyone else?
what was your car length setting? at that speed you want to be around 5
 

KG2V

Member
Mar 9, 2019
206
163
Bayside, NY
It is why I won't use AP in fast moving heavy traffic. I'll ONLY use it in bumper to bumper 5-15 mph traffic (then usually set to a 1-3) or on the open road, and then set to 7

I think it is actually dangerous in the 40-50 slowing to Stop, to 40-50 MPH range due to the hard braking - the car just isn't smooth
 
  • Disagree
Reactions: NoMoGas

BZM3

Member
Aug 15, 2019
281
183
Somewhere
I don't know.. I commute every day on the highway and my AP is smooth as butter. Rarely does it get jumpy and only in reasonable scenarios that it has to act quickly.
 
  • Like
Reactions: NoMoGas

am_dmd

Member
Jan 29, 2017
303
345
PA
I too have experienced hard braking. I think problem is because Tesla uses "time" based instead of "car length" like every other cruise control. Many times I have seen even if I select 1 out 7 it keeps a big distance between car in front and my car.
 

Chisale

Member
Sep 28, 2019
244
248
Ohio
The only problem I've had with AP is when someone turns left or right in front of you and then there's a hill up ahead. Seems to take too long to figure out that nobody is there and it's safe to proceed. Never had one problem with braking though I also keep the following distance on the high side. But the overall moral of your story is you can drive dozens of miles alone with no issues whatsoever. But when family is present and you're showing off the features; that's when something is going to go wrong.
 
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Reactions: agtdDelirium

⚡️ELECTROMAN⚡️

Safety Score of 97 and steady
Jul 15, 2016
2,876
5,453
Pacific Northwest
I think it waits too long to start decelerating and then brakes too hard too early. It doesn’t brake smooth and human like which I think has more potential to catch the driver behind you off guard. I thought I was pretty close to being rear ended earlier today. I hit the accelerator to avoid getting hit.
 

quickstrike12

Member
Jun 13, 2018
642
498
Fort Worth Texas
It’s called “hysteresis” it’s the software version of a set point on the way up (speeding up) and the deceleration (way down) it has different values. Doesn’t matter if it’s speed or distance based or a formulation of both, the final value is X to the car. They obviously are set to tight and it needs a buffer or cushion between the two. Let’s say the perfect distance the car wants to keep is X (based on the speed). It can’t use that EXACT number for acceleration and decel perfectly because if it tried it would be on and off the gas several times a second trying to be perfect. Human don’t drive like this either. So they use a number like X+ some value to the high side and X- some number to the lower side. A buffer if you will around the perfect distance. Humans do this without thinking about it. We sacrifice some of our follow distance when everyone is slowing and stopping to be smooth and also not to shock cars behind us. The APs hysterisis is set to too tight and needs to be opened up. At least on the deceleration side a bit. It’s hard tho because computers can’t see clues around them and deduce everyone is about to be coming to a stop, based on all the brake lights far ahead, emergency vehicles and many other clues. We have been driving all our lives and learned to sense these clues and anticipate what’s happening and how sudden people are beginning to stop. The AP only has a number X to work with and that’s it.

The issue is relatively easy to fix for Tesla I think, if they wanted to. Not sure why they don’t honestly. It always felt to me like the engineers and Elon himself don’t use the AP in day to day traffic and real world scenarios like the rest of us or they surely would see this.
I would have thought that higher following settings like 5,6 or even 7 would utilize this extra space to come to a smooth gentle stop by sacrificing more of the perfect X follow distance.
 
Last edited:

Mo City

Active Member
Jul 17, 2016
1,910
11,883
near Houston
Hard, unnecessary braking is far and away my biggest problem with autopilot. I'm assuming this will be fixed when medium speed FSD is released in coming months. Otherwise, it will be a huge letdown for me.

As someone said earlier, I use AP mainly in bumper to bumper highway traffic, where it totally rocks!
 

quickstrike12

Member
Jun 13, 2018
642
498
Fort Worth Texas
As I understand it. The current software design is not written to take advantage of the newer HW3 chips yet. It will most likely be a completely different code from the ground up to take advantage of the speed and ability to process information. it’s quite possible that current implementation of software using HW 2 and 2.5 just can’t do the things we need.
I feel like they are just limping it along long enough for them to finish the new code and to have a sound plan in place to upgrade the older cars. No small feet.
 

VT_EE

Active Member
Apr 22, 2017
2,077
2,777
Maryland
As I understand it. The current software design is not written to take advantage of the newer HW3 chips yet. It will most likely be a completely different code from the ground up to take advantage of the speed and ability to process information. it’s quite possible that current implementation of software using HW 2 and 2.5 just can’t do the things we need.
I feel like they are just limping it along long enough for them to finish the new code and to have a sound plan in place to upgrade the older cars. No small feet.
This is highly plausible. I’m expecting a totally different experience when the real FSD load is out running on HW3.
 

Perzivel

Member
Oct 25, 2019
29
6
Boston
What I find incredible is that we never have or see actual engineers that work on this stuff, post about it here! I figure that this is such a new technology and those in the field would be so excited to share their experiences and desires that they would be in here explaining why we have our gripes.
 

quickstrike12

Member
Jun 13, 2018
642
498
Fort Worth Texas
What I find incredible is that we never have or see actual engineers that work on this stuff, post about it here! I figure that this is such a new technology and those in the field would be so excited to share their experiences and desires that they would be in here explaining why we have our gripes.
Man that would be awesome. My guess is many of them would love to, but it may be a company policy not to. Possibly fear of letting out news or changes unintentionally before they are ready.
 

johnnyS

Member
Sep 8, 2011
585
196
If I am in the carpool/HOV lane and the regular lanes are 10-20 mph slower autopilot brakes on an outside curve which can be dangerous. I do not use it a lot as a result.
 

Mo City

Active Member
Jul 17, 2016
1,910
11,883
near Houston
What I find incredible is that we never have or see actual engineers that work on this stuff, post about it here! I figure that this is such a new technology and those in the field would be so excited to share their experiences and desires that they would be in here explaining why we have our gripes.
Whether Tesla, Waymo, Mobileye, GM, Ford, Apple or whoever, secrecy rules for self-driving technology. There is a big pot of gold for the company that breaks through first, especially if it takes a while for others to follow.

Tesla is far more open than any of the others.
 

aerodyne

Nose cone car - "Going to LR"
Nov 19, 2018
3,136
4,137
Los Angeles
What I find incredible is that we never have or see actual engineers that work on this stuff, post about it here! I figure that this is such a new technology and those in the field would be so excited to share their experiences and desires that they would be in here explaining why we have our gripes.
One word...NDA's
 

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