# NON-phantom braking



## MJJ (Aug 7, 2016)

I posed this question in the FSD thread which in hindsight wasn't the correct place to put it. Reposting here for wider exposure.

We have endless conversation about braking that occurs during TACC or AP which seems to have no apparent cause. I have undesired braking, but in the cases I'm describing, I can see exactly the cause. I'm hoping if I describe them, others will either chime in, or will tell me it's my car only.

On the freeway, in very specific geographic locations, the car will suddenly acquire a lock on a vehicle in an adjacent lane. If we are passing them, the brakes are suddenly applied, as hard as during a "phantom" event, and left uncorrected we end up pacing the vehicle just adjacent to the rear bumper. It may occur when the vehicle is to the left, or to the right, of me. I think everyone is familiar with the tint change of the vehicle in the visualization when a speed lock actuates. Maybe "speed lock" is not the correct term, but I think it's descriptive. There is no reason I can think of why such a lock would be necessary in these cases.

There is no correlation with potential merge zones. The main place this occurs is in a town, so there are many on and off ramps and it does occur adjacent to these, but it also occurs along clear stretches of straight lane open road with no potential side traffic. In this specific location, the issue began within the last few months, but there is another location where it has occurred consistently for three years.

If you have a sense that this is happening to you, this is the thread to mention it in. I'm hoping we can draw some attention to it. I do press the FSD snapshot button but I fear it's disregarded due to it being during operation of the non-FSD mode. 

Thanks

PS. I suppose it should be said: Please do not discuss random phantom braking in this thread. The title is "NON-phantom."


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## SoFlaModel3 (Apr 15, 2017)

I find that this is the car's logic when you're going faster than the car next to you, so it slows for safety. Personally I absolutely hate it and find it to be terribly annoying. If you have someone behind you it can be unsafe as well. I just mash on the accelerator until I'm clear of the slower moving car to the left or right.


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## M3OC Rules (Nov 18, 2016)

If it's dark than its yielding to that car and thinks they are going to merge. Sometimes I think it just makes very poor decisions. I agree I have seen cases where there is no way for that car to merge so it doesn't take into consideration where the lanes go. Perhaps this will change to different code when they go to the single stack FSD Beta so they aren't working on fixing it in the AP code.


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## MJJ (Aug 7, 2016)

SoFlaModel3 said:


> I find that this is the car's logic when you're going faster than the car next to you, so it slows for safety.


As a rule, I generally fly past slower traffic without any slowing (the right-lane precautionary slowing aside, but that's well marked on the visualization). I would not characterize the behavior as being part of a feature.


M3OC Rules said:


> If it's dark than its yielding to that car and thinks they are going to merge.


Yielding, yes. The expectation of merging, is not consistent with the surroundings.

It sounds like you both are experiencing this, which is a relief. It's not just me. But can you please be aware and when it happens, see if you notice that the nearby vehicle has suddenly changed to "yield" or "lock" status? And post up.

I also wonder if this is one of those things that will just go away with the single mode for street and highway. Let's hope.


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## M3OC Rules (Nov 18, 2016)

MJJ said:


> Yielding, yes. The expectation of merging, is not consistent with the surroundings.


When I said poor decisions I meant really poor. Like cases where there is a frontage road that doesn't connect or an exit. And sometimes you're past the car which also doesn't make sense.


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## JasonF (Oct 26, 2018)

AP is reacting to a change in acceleration of the car next to you. AP is a bit paranoid, and looks for any sign that the driver next to you might be preparing to change lanes suddenly or turn suddenly. If the other car changed acceleration suddenly, that’s one of the signs (others include the other car getting close to the lane lines). I notice that because I’m nearly as paranoid a driver as AP is, and I also react to another driver slowing or accelerating suddenly!


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## MJJ (Aug 7, 2016)

JasonF said:


> AP is reacting to a change in acceleration of the car next to you.


I believe it is not. As I say, the behavior is specific to certain locations only. As such, I keep a keen eye on the visualization in these areas. I am familiar with the reaction to converging course traffic and this is not happening. Nobody is making any sudden moves. I am usually passing, being in a passing lane, but I can be pacing as well. Suddenly the other vehicles tint changes, my car makes an abrupt braking maneuver, and aligns itself just off their rear bumper. I repeat: this is happening when there is no reason for it to be.


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## JasonF (Oct 26, 2018)

MJJ said:


> I believe it is not. As I say, the behavior is specific to certain locations only. As such, I keep a keen eye on the visualization in these areas. I am familiar with the reaction to converging course traffic and this is not happening. Nobody is making any sudden moves. I am usually passing, being in a passing lane, but I can be pacing as well. Suddenly the other vehicles tint changes, my car makes an abrupt braking maneuver, and aligns itself just off their rear bumper. I repeat: this is happening when there is no reason for it to be.


There also might be subtle roadside cues that cause drivers to move closer to you, slow abruptly, or something like that in those locations. It could be as simple as the lane narrowing a few inches there, or the perception of the lane narrowing due to guardrails or signs.


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## MJJ (Aug 7, 2016)

I’ve had another similar incident today. An apparent “phantom” braking on the freeway. I’m training myself to look immediately at the screen and sure enough, I caught FSD with a lock on a vehicle which had exited the freeway on an off ramp. It was a good 300 feet down the off ramp and about 100 feet away from us, on a divergent course. If you experience a phantom brake, check your display. I’ll bet you’ll start to notice nonsensical locks on innocuous vehicles.


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## MJJ (Aug 7, 2016)

I am going to bump this every time there is a new release. Until the problem is fixed of course.

Behavior continues on FSD 10.8.


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## Mike (Apr 4, 2016)

As I mentioned in another thread, for the first time in months, I had NOA lock onto a slower vehicle to my right.

I’m on 44.25.2


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