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Accident averted, but that leaves more unanswered questions.

I expect that under normal circumstances, the car gives advance notice of the lane change to comply with traffic regulations and/or to give the driver time to cancel the maneuver. In an emergency situation, delay is unnecessary.

Yeah, FSD beta sometimes changes lanes without a turn signal which is a fun keep your head on a swivel moment.
 
Perhaps you missed my previous post... can you please answer the following question? Are you saying that you let your foot off the brake and THEN AP made the lane change and continued through the light, or that it made the lane change while you still had your foot on the brake?
Sorry I missed your question. No, i did not take my foot off, I was flooring it, and the car slowed down considerably, but when it was a few feet behind the other one, I pressed the brake even harder wanting the car to stop asap, but it accelerated slightly and switched lane at the same time very smoothly but rapidly, did not feel like unintended acceleration at all, that would have freaked me out even more, felt like how AP would sometimes accelerate before a lane change. But the lane change was swift, it did not slowly merge into the other lane.
 

KArnold

Active Member
May 21, 2017
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Columbus OH
I pressed the brake even harder wanting the car to stop asap, but it accelerated slightly and switched lane at the same time very smoothly but rapidly
Hmmm, not sure it can continue to accelerate or auto-change lanes once the brake is tapped. At least as I understand it.

FSDb will indeed quickly and safely change lanes on occasion, as needed. Had one yesterday, 2 lanes about 45-MPH, I'm behind someone in the left lane. FSDb is at set speed and happy where it is. The lead car signals a left turn and slows - FSDb made an immediate and somewhat aggressive (although very safe) change to the right lane.
 
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Supcom

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Oct 3, 2021
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Sorry I missed your question. No, i did not take my foot off, I was flooring it, and the car slowed down considerably, but when it was a few feet behind the other one, I pressed the brake even harder wanting the car to stop asap, but it accelerated slightly and switched lane at the same time very smoothly but rapidly, did not feel like unintended acceleration at all, that would have freaked me out even more, felt like how AP would sometimes accelerate before a lane change. But the lane change was swift, it did not slowly merge into the other lane.
Your description sounds like the car calculated that it could not brake quickly enough to avoid running into the car ahead, so used the accelerator to overpower the brakes while changing lanes. Curious maneuver since I would expect most people to have a death grip on the wheel that would prevent the car from turning. Clearly this was not the case per your description of events. But accelerating without guaranteed steering would have ensured a worse collision, so the car must be able to ignore the driver input to ensure the maneuver can be executed successfully.

Assuming this is so, it's both impressive and quite scary at the same time. It also seems that Tesla should disclose the existence of such a feature. At the very minimum, I would hope that the notification history in the car would have an entry for this event!
 
Sorry I missed your question. No, i did not take my foot off, I was flooring it, and the car slowed down considerably, but when it was a few feet behind the other one, I pressed the brake even harder wanting the car to stop asap, but it accelerated slightly and switched lane at the same time very smoothly but rapidly, did not feel like unintended acceleration at all, that would have freaked me out even more, felt like how AP would sometimes accelerate before a lane change. But the lane change was swift, it did not slowly merge into the other lane.

No problem. Unfortunately I think we are all going to be at a loss of any reasonable opinion because your statements are implying multiple things that I think most people are going to at least assume cannot happen(as designed). Please don't get me wrong, I'm not going to sit here and say that what you are saying did not or could not have happened, it just seems very unlikely for the reasons below.

Brake override. I would be surprised if Tesla is not allowing brake override in all situations on purpose. While it is not a legal requirement to have a brake override system, I think people and NHTSA would have a major issue with your scenario as described.

In a possible rear end collision scenario I think the normal operation would be for the car to just apply AEB(automatic emergency braking). Now if you were on and stayed on AP then I could possibly see an avoidance maneuver BUT...

You pressed the brake pedal which would have automatically disengaged TACC and AP auto steer. You also kept the brake pedal pressed which would presumably preclude any acceleration event for two reasons. It would either have to apply acceleration while the brakes were still engaged OR it would have to override the user's brake input. Override the users brake input I think would be extremely frowned upon and most likely would open up Tesla for liability. Engaging acceleration while also allowing the users brake input is more believable, however; that means the car has to add a considerable amount of power to accelerate through the friction brakes which then open up a massive "uncontrolled" acceleration boost if the user suddenly lets off the brake.

There is a lot here that doesn't make sense. Could the car be programmed to do what you perceived happened, sure. Do I think it happened the way you said it happened, sadly no. It is a shame you don't have a dashcam video. You should enable dashcam save on honk. Also if you have a situation like that again just hit the dashcam button and it will save a clip on demand.
 

Supcom

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Oct 3, 2021
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Override the users brake input I think would be extremely frowned upon and most likely would open up Tesla for liability.
From what I have seen of the the Tesla brake system, the car cannot override driver brake application by disabling them. It can only do this by overpowering them with the motors. The brake system is designed such that the brake pedal will always apply brakes. But, like any car, the motors are more powerful than the brakes.
 
From what I have seen of the the Tesla brake system, the car cannot override driver brake application by disabling them. It can only do this by overpowering them with the motors. The brake system is designed such that the brake pedal will always apply brakes. But, like any car, the motors are more powerful than the brakes.

Correct me if I am wrong but isn't the brake pedal strictly electrically controlled, meaning there is no physical mechanical linkage to the friction brakes? If there is a mechanical linkage then I totally agree with you, but if it is strictly electronically controlled then software could override user input...technically. Now do I believe that anyone would actually specifically program that functionality, NO.
 
It is a shame you don't have a dashcam video. You should enable dashcam save on honk. Also if you have a situation like that again just hit the dashcam button and it will save a clip on demand.
I have dashcam on honk, but I never honked. I never honk, it only worsens the situation. If I hit dashcam button manually, does it recapture few seconds/minutes into the past or will only record from that point onward? Not that anywoudl wold have time to press it in such a situation, just asking for clarification.
 

Supcom

Active Member
Oct 3, 2021
1,393
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Texas
Correct me if I am wrong but isn't the brake pedal strictly electrically controlled, meaning there is no physical mechanical linkage to the friction brakes? If there is a mechanical linkage then I totally agree with you, but if it is strictly electronically controlled then software could override user input...technically. Now do I believe that anyone would actually specifically program that functionality, NO.
When you push the brake pedal, you are directly pushing on the brake reservoir piston. It's a safety thing so you can always stop the car, even if there is a total power/computer failure. The car can also depress the pedal in parallel with you, but cannot prevent you from activating the brakes. If you do lose power, you will also lose the brake boost, so it will take more braking force.

The accelerator generates an electrical signal that is used by the car's computer to control engine speed. So, the car could ignore your input.
 
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I learned a new thing about Tesla recently - holding down the park button on the stalk engages the rear brakes in an emergency mode should the front brakes fail for some reason. It's recommended to pulse them instead of just holding down the button constantly, as the braking is very intense/jarring. Hold the button until you feel the car braking, then release, then push back down again until you feel the brake, then release and do this until the car comes to a stop.
 
I learned a new thing about Tesla recently - holding down the park button on the stalk engages the rear brakes in an emergency mode should the front brakes fail for some reason. It's recommended to pulse them instead of just holding down the button constantly, as the braking is very intense/jarring. Hold the button until you feel the car braking, then release, then push back down again until you feel the brake, then release and do this until the car comes to a stop.
The manual said, (or used to say?), to use that only in emergency, as it could damage the car? I was never clear on what the damage might actually be?
 
The manual said, (or used to say?), to use that only in emergency, as it could damage the car? I was never clear on what the damage might actually be?
I don't think it damages the car, it just engages the rear brakes when held down. When we press the brake pedal, it's almost entirely the front brakes that are engaged, the rear brakes are typically only engaged for parking (you hear that electrical motor sound as the rear brakes are engaged).

 
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When you push the brake pedal, you are directly pushing on the brake reservoir piston. It's a safety thing so you can always stop the car, even if there is a total power/computer failure. The car can also depress the pedal in parallel with you, but cannot prevent you from activating the brakes. If you do lose power, you will also lose the brake boost, so it will take more braking force.

The accelerator generates an electrical signal that is used by the car's computer to control engine speed. So, the car could ignore your input.
Got it, so yeah the car could attempt to overpower the users brake engagement but that would be a major liability issue for Tesla.
 

brkaus

Well-Known Member
Jul 8, 2014
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Austin, TX
It could be ABS activating. If the tires started to slip, ABS would kick in and modulate the braking force.

The quick release of the brakes will feel like acceleration. In reality is is reducing the rate of deceleration.

I used to experience this sensation on my truck. Did a bit of experimenting in a safe area to confirm what was happening in my case.
 

Dan D.

Desperately Seeking Sapience
Dec 7, 2020
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I learned a new thing about Tesla recently - holding down the park button on the stalk engages the rear brakes in an emergency mode should the front brakes fail for some reason. It's recommended to pulse them instead of just holding down the button constantly, as the braking is very intense/jarring. Hold the button until you feel the car braking, then release, then push back down again until you feel the brake, then release and do this until the car comes to a stop.
The emergency stalk button could be ignored, over-ridden, or fail to work due to software flaw. Not implying it has ever been. How do stalk-less cars engage this function, and if the answer is touchscreen is there a backup if the touchscreen has failed?

So summing up:

  • Main brake system is mechanical (user pedal)
  • Main brake system can be electrically applied (car intent)
  • Main brake system can be released electrically (ABS pulse or arguably fully released/degraded due to ABS fault, unknown if ABS can be overridden or brakes fully released by software control)
  • Rear brakes can be electrically applied by the stalk (user's intent) or by the software (car's intent)
  • Stalk signal could be ignored or fail to work
  • No mechanical option for parking brake
  • Brakes can fail mechanically

Most of these are not unique to Tesla cars of course.

Also, brakes may or may not disengage certain control modes like TACC, Autosteer, etc at certain speeds or in certain situations. There seem to be anecdotal stories of odd things happening that the driver was not expecting. There could be overriding intentional decisions or software flaws in the car. It would be nice to have all control decisions explained by Tesla.
 
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Override the users brake input I think would be extremely frowned upon and most likely would open up Tesla for liability. Engaging acceleration while also allowing the users brake input is more believable, however; that means the car has to add a considerable amount of power to accelerate through the friction brakes which then open up a massive "uncontrolled" acceleration boost if the user suddenly lets off the brake.
What could have happened: through muscle memory, I stepped off the brake either to pump it or if I felt I had stopped and won't hit the car, and in that instant, the vehicle accelerated and switched lanes.

I don't remember exactly, most of what I did was muscle memory and instincts not a carefully thought-out action.

Hitting honk within 10 mins is a good thing I learned today.
 

KArnold

Active Member
May 21, 2017
1,219
1,412
Columbus OH
What could have happened: through muscle memory, I stepped off the brake either to pump it or if I felt I had stopped and won't hit the car, and in that instant, the vehicle accelerated and switched lanes.
Not conclusive of course, but if you did not manually engage the brake, perhaps because FSD already was, it would explain the rest - that's "working as designed". FSD has demonstrated the ability to very, very quickly decide/signal/engage/accelerate a lane change when the situation warrants.
 

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