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AP locking onto cars in the other lane and slowing down to their speed

Aug 22, 2019
20
18
MD USA
I'm sure this has been discussed. But when I search for phantom braking, all I'm finding is stuff about AEB, bridges, shadows, etc.

You know how the UI shows the surrounding traffic, and lights up the vehicle it is following or targeting or whatever you want to call it? During the day, that target vehicle or vehicles light up dark black. And in night mode, those target vehicles are lit up white. While all other non-target vehicles are just grey.

Let's say I'm in the left lane operating in TACC or AP. The car in front of me will be lit up as the target it's following. Then for reasons I can't understand, it will light up a vehicle in the lane next to me and slow down to match that vehicle's speed as if it is in my way. This is rather exciting if the lane next to me is moving slower or stopped. In stop and go traffic, my lane could go but the other lane is still stopped so I don't go. Or let's say I'm going 70 and the lane next to me is going 60, all of a sudden the car drops to 60 to "follow" that car in the other lane.

It doesn't do it all the time. And I can't find any reasonable common circumstance. The lane markings are all really good. There are no mistakable things like seams in the pavement. The car in the other lane is not drifting towards me or signalling. There is no actual real reason in reality for it to think that vehicle in the other lane should be a target to follow. The UI even shows it over in the other lane completely.

Has there been any official or unofficial explanation for this behavior? I can only assume it is some fusion error between the camera vision and radar vision not lining up. But it shows it lined up on the UI.
 
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Pale_Rider

Member
Jul 28, 2016
673
749
Houston, TX
I think they are trying to get the car to recognize when an adjacent car is about to cross into your lane, either to change lanes or just due to distraction. They mentioned something about this at the autonomy day. It could be that car made a subtle move towards your lane and that movement was misinterpreted. Or maybe its just flaky lol.
 

vescrig

Member
Dec 21, 2017
31
17
Spain
Are you positive this happens when you are in the *left* lane? Here in Europe, the car behaves this way because it's illegal to overtake on the right.

Yes, fully positive.
It happens in both lanes. I understand that's the right behavior when I'm in the right lane, but when I'm in the left one, passing another vehicle, at some point AP decides that is "traffic" and shows it in bright white, adjusting the speed to the vehicle at the right.
 

S4WRXTTCS

Well-Known Member
May 3, 2015
5,454
6,202
Snohomish, WA
I really wish they'd allow more fine-grained control over this.

The vast majority of the time I use TACC only, and I fail to see why it needs to aggressively slow down for vehicles adjacent to me. I mean I am controlling the steering so obviously I'm paying attention.

I don't need or want TACC to try to be smarter than the bare minimum.
 
Aug 22, 2019
20
18
MD USA
I don't think it does need to slow down for vehicles adjacent to you. I'm pretty sure that isn't actually what it is trying to do. It is for some reason detecting that adjacent vehicle as a current or imminent traffic conflict, just like the vehicle in your lane that you're following. I believe it is a false positive, probably due to some sensor limitation or sensor fusion complication. The display on the UI is likely vastly over-simplifying what it's really seeing and thinking, so we're not seeing what it really thinks.
 
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paaltio

Member
Feb 16, 2019
53
40
Finland
For me AP seems to randomly detect merging vehicles, showing them with a darker color on the right, and try to match their speed so they can merge safely. This happens way before they've started to cross the lane, or even turned on their signal sometimes. This can produce pretty violent braking at times. It seems like it uses map data to determine where the junctions are and then adjusts the behavior for cars on the right. I don't have it happen in regular highway driving when passing cars.
 

Tjhappel

Member
Dec 12, 2014
254
344
San Clemente, California
During the fsd day presentation Karpathy touched on this saying it’s the computer guessing what the car in front would do based on what it had been doing. This is a known issue ams they’re definitely making progress imo on the slamming brakes for no reason when the driver is only even on a line.

Has anyone noticed it happen on the left side of vehicle? To me it’s never happened except when I’m in carpool lane and someone creeps over int it.
 
Aug 22, 2019
20
18
MD USA
I think I figured what is going on in every circumstance where this has happened. It's because it thinks the lane is ending and I need to merge!

i was watching the display in detail and found it was even lighting up target vehicles that were coming up behind me in the next lane. That tells me it was doing it very intentionally, as that vehicle would obviously not be a forward collision threat. Then I started thinking about exactly where I've been experiencing this issue.

Every location I experience this is where there are special lane markings for HOV. Which are short thick dashed lines. I believe it is confusing these with the other similar looking lane markings indicating the lane is coming to an end you need to merge over. Makes perfect sense now. This also explains why it only ever happens when I'm in the left lane. Because that's the HOV lane everywhere around here.

So I no longer believe this is the system mistakenly thinking these cars in it's way and it needs to not hit them. It's actually being really smart under the mistaken believe that I need to merge.
 

widodh

Model S 85 and 100D
Jan 23, 2011
6,853
2,773
Venlo, NL
I just drove 60km to Amsterdam over a very new highway with super clear markings. For those interested, this was the route: Google Maps

So this kept happening to me, not only today, but also in the last weeks. I'm on 2019.32.2.2 with my S100D right now.

What I noticed is that the car in the lane right of me was slightly moving towards the markings, but it was still between them. The driver wasn't driving in the exact center of the lane, but slightly more to the left.

This causes AP to 'mark' that car and then match it's speed. Super annoying.

I also had this with a lane change where it thought my lane suddenly wasn't clear to move in to because it thought a car even more lanes to the left was in my lane.

The lanes were not special or ending. 4 lanes going towards Amsterdam.
 

brkwtz

Member
Jun 28, 2016
35
8
Los Angeles
Interesting discussion. I have AP1 and for the last few weeks it has been doing this too. My conversation is that it occurs when a car was in your lane ahead and then has moved on, but the computer was busy with some other process and now is finally get to the process that should have conducted a few seconds before. This is not good, as certain functions should have higher priority over others for execution.
 
Aug 22, 2019
20
18
MD USA
Interesting discussion. I have AP1 and for the last few weeks it has been doing this too. My conversation is that it occurs when a car was in your lane ahead and then has moved on, but the computer was busy with some other process and now is finally get to the process that should have conducted a few seconds before. This is not good, as certain functions should have higher priority over others for execution.
That's certainly not what is going on. It doesn't work like that. Unless you have some actual evidence, I think you misunderstand how computers work.
 

brkwtz

Member
Jun 28, 2016
35
8
Los Angeles
That's certainly not what is going on. It doesn't work like that. Unless you have some actual evidence, I think you misunderstand how computers work.

Actually that is exactly how computers work. Another case in point, when using the turn signal to make a lane change, the first time executed since the car has been started takes twice as long for the computer to decide its OK to execute the lance change. Subsequent lane changes are made considerably faster. The computer on the initial lane change needs to load into memory the functions needed to execute the lane change first before actually processing the lane This computer 101.
 

murc585

Member
Jun 27, 2019
94
123
Canada
I think I figured what is going on in every circumstance where this has happened. It's because it thinks the lane is ending and I need to merge!

i was watching the display in detail and found it was even lighting up target vehicles that were coming up behind me in the next lane. That tells me it was doing it very intentionally, as that vehicle would obviously not be a forward collision threat. Then I started thinking about exactly where I've been experiencing this issue.

Every location I experience this is where there are special lane markings for HOV. Which are short thick dashed lines. I believe it is confusing these with the other similar looking lane markings indicating the lane is coming to an end you need to merge over. Makes perfect sense now. This also explains why it only ever happens when I'm in the left lane. Because that's the HOV lane everywhere around here.

So I no longer believe this is the system mistakenly thinking these cars in it's way and it needs to not hit them. It's actually being really smart under the mistaken believe that I need to merge.

I support this theory as I can replicate it in the same location everyday. On the highway I take to work, we have this weird system where a big truck move a cement barrier left/right of the lane to allow for 2-3 lanes per direction, based on the time of the day.
Lane markings are present on the left lane that make it seem as if the lane was ending, which is not the case.
The car seems to get stuck into this mode until I get off this section of the highway. It seems to detect it earlier than I can see it sometimes which also makes me think GPS data is affecting its behavior, although I know how farfetched this sounds.
If I stay in the center lane, no issue.

This has also happened to me on a long on-ramp while I was stuck in heavy traffic. I was on autopilot and the car must have gotten a glimpse of the end of the on-ramp (or the GPS thing) and locked onto a stopped car besides me. I have never had so much coffee fly onto my shirt, autopilot had never done this to me before. This may be a coincidence but this happened the morning after an update to 2019.32.2.1, I don't remember my car doing this before. I really wonder if it's using mapping data from NoA?
 

mrkisskiss

Member
Jan 26, 2017
232
281
London
This happens to me frequently, and is one of the major regressions of Autopilot, along with increased "phantom" and micro braking.

In fact, it's an extremely dangerous regression. For me, this will happen sometimes (but not always) when overtaking a car: the Tesla will suddenly decide it wants to match the speed of the car as you're overtaking. This results in the Tesla slamming on the brakes, just as you're alongside the other car, which is unpredictable and quite dangerous for those around me... and uncomfortable and alarming for me and my passengers.

I've spent two years "explaining" random AP behaviour to concerned passengers, but I'm finally bored of it. It's gone from a system that was dumb enough to be predictable, yet mostly fit for purpose, to a system that's actively dangerous and unpredictable even when working as intended. I don't expect it to improve on my car.

I think the biggest single "feature" that's responsible for the majority of these regressions is the "cut in detection", which clearly doesn't work very well, at least not in the UK where roads are narrower, and there is apparently a penchant for driving relatively close to the outer lane line (I'd never noticed how common it is - until now)
 
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