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TACC failed to brake at stop, nearly accident.

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I was showing a friend TACC and how it works/performs over the weekend and during a mundane red light stop, the TACC failed to brake properly and we almost ended up rear ending the car in front of us. Needless to say, she was less than impressed.

I have a dash cam and recorded it here: P85D TACC fails to brake at red light. Almost accident. - YouTube


It's hard to tell but we were going at a decent but manageable speed and was following the blue Prius in front of us. The TACC was on and i did not manually step on the brakes at all, even until the end. Had I not swerved to the right, we would have rear ended the car. It appears that at that situation, TACC might have thought the road curved to the right given that the vehicle in front of me started going towards the right and also the lane opens up as well. It did not take notice on all the vehicles that have stopped and also the vehicle in front of us that has been stopped.

So guys, be careful using TACC, especially if the car in front of you is leaving the lane. It seems that TACC does not track or does not like to track anything beyond the vehicle in front of you.
 
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Interesting.

Does anyone know if the system learns from events like this. As in, was this data collected and uploaded to Tesla, to further enhance TACC. I kind of assumed drivers are basically guinea pigs for the TACC system...but is that true?
 
Infinity claims their Q50 system looks at the car in front of the car that is in front of you to see what it is doing.
That seems ambitious. Is the Q50 tall enough to always see over the car in front?

I believe this is done by glancing radar on the road underneath the car in front of you to see further ahead. I'd guess the Tesla hardware has this capability, though not sure if they're using it. I also wonder how that works when all cars are using a similar system.
 
That's very interesting, and a little scary.

So bottom line, the TACC still needs to be babysat just as if you were doing the driving yourself. Sounds like the only thing it saves is a little calf-fatigue of the constant breaking and accelerating, not that I was going to be reading a book in traffic, but I thought it would be a little more fool proof than this. Hoping Tesla continues to fine tune it and prevent things like this.

Kudos to you for avoiding the accident and the resulting headache of getting it fixed.
 
Looks to me like TACC didn't stop because it didn't switch radar lock from one vehicle to the other when the first vehicle turned off, however Emergency braking did work.

I know you state that you would have hit the vehicle in front, however in the video it appears that the emergency braking managed to stop you just short (though I'll admit it wasn't a comfortable distance)

Seems to me that TACC could switch vehicle radar lock faster, but that emergency braking worked properly.
 
Not making excuses for the TACC, but this is a fairly standard failure mode for TACC. The same thing would happen if you came up in cruise control to a stop light where a car was parked for the red. In other words, had the blue car not been there at all, you would have run into the stationary white car anyhow. TACC does not see stationary objects and it would happily plow into the back of it until emergency braking kicked in. That is essentially what happened here. The blue car cleared your lane so TACC thought it was free to accelerate to cruise speed and TACC will not stop for the stationary white car. Had the white car still been moving, it would have locked onto it and stopped.

It does appear that emergency braking would have managed to stop the car before contact was made, but just barely.
 
Not making excuses for the TACC, but this is a fairly standard failure mode for TACC. The same thing would happen if you came up in cruise control to a stop light where a car was parked for the red. In other words, had the blue car not been there at all, you would have run into the stationary white car anyhow. TACC does not see stationary objects and it would happily plow into the back of it until emergency braking kicked in. That is essentially what happened here. The blue car cleared your lane so TACC thought it was free to accelerate to cruise speed and TACC will not stop for the stationary white car. Had the white car still been moving, it would have locked onto it and stopped.

It does appear that emergency braking would have managed to stop the car before contact was made, but just barely.

TACC does not see stationary objects? That's not been my experience. That also means stop-and-go traffic wouldn't work, which it does.

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So bottom line, the TACC still needs to be babysat just as if you were doing the driving yourself.

That's always going to be the case, no matter how good it gets. The difference is you have more attention to spend on your surroundings if you aren't wasting effort modulating car inputs.