# AP/TACC Stop and Go Behavior



## gary in NY (Dec 2, 2018)

I've noticed that when my car is following behind another while in AP or TACC, and that car slows and turns off, my car wants to almost come to a complete stop, sometimes hesitating or even making a false start to get back up to speed. This is even though the turning car has cleared the lane and moved on. This isn't so much an issue for me, but the cars behind me are anticipating that my car is going to react the way most normal cars do, so they prepare to speed back up. But I'm not moving as fast as they anticipate, which causes them the stop short, sound the horn, yell obsinities, etc.. In the worse case they could rear end my car. Of course they are following too closely if they hit me, but I'd rather not be in that situation at all.

This happened today when a F-150 was following me closely, and the car in front slowed to turn right onto a side road. AP nearly stopped, did a false start, then started back up again. The F-150, was nearly in my trunk after this. A short time later while in TACC, the car did basically the same thing. This time there was no car following me. I did not think to save the dashcam video in either case, but I will try the next time this happens.

I have the following distance set to the max, but I wish it allowed a more space between me and the leading car. Would a greater distance allow the car to react "normally"? This is really annoying behavior

Edit: V - 2019.8.3


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## GDN (Oct 30, 2017)

I almost feel you need to go the opposite way with your follow distance. I never use more than 3 and more typically I'm only on 1 or 2. I've seen some of the hesitation, but only slightly after a car moves from in front of me. Set at the max distance it is finding other things or surveying the scene to know whether or not the path is clear. Try the lower follow distance settings and see if you don't have a better experience.


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## Bokonon (Apr 13, 2017)

I second @GDN's suggestion -- try using a shorter following distance in gridlock, even if you prefer a larger distance at speed. It may be possible that the current parameters for max TACC distance cause unexpected behavior in gridlock.

Anecdote:

On my commute home Friday, TACC seemed "off" to me -- it was less responsive when a stopped car ahead starting to move again, and wanted to stop much sooner (and much more abruptly) when the car ahead stopped. I don't remember it "stuttering" like @gary in NY described, but starting and stopping in traffic felt far less "human" than it usually does.

At some point, I checked the follow distance setting, and was surprised to see it at 7, rather than its usual 3. After bumping it back up to 3, TACC resumed what I would call "normal" behavior.


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## shareef777 (Mar 10, 2019)

I have the same exact experience. Kinda used to it as my previous 2018 Honda Accord with ACC (adaptive cruise control) would do the same exact thing. What I’ve learned to do is to lightly tap my accelerator as soon as a car has cleared the lane ahead of me until CC recognizes that there’s no obstacle ahead of me (essentially over/riding the vehicles cruise control temporarily).


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## SoFlaModel3 (Apr 15, 2017)

At higher speeds I keep my cruise follow set to 3. Anything more and I get passed too much. As speeds lower and traffic comes into play I bring that down to 2 and ultimately 1. Also any time the car doesn’t get the acceleration correct you can step on the accelerator pedal and bring it up to speed faster!


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## gary in NY (Dec 2, 2018)

I'll add the road/traffic details to the post above.

Very interesting suggestions. I had thought about hitting the accelerator as soon as the car ahead turned because I had seen this reaction before, and in the first case with the pick-up following so close, thought I might need to. I drive mainly on rural roads, and rarely see anything resembling gridlock, but I'm going to try changing the following distance and see what happens. It will be an interesting experiment.


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## DocScott (Mar 6, 2019)

I also see something like this when a car does a rapid cross from left to right in front of me, whether it's someone doing a crazy multiple-lane change or just someone driving across on a cross-street. AP doesn't seem to trust that the crossing vehicle has really cleared my lane even after it has, and also doesn't seem to realize that the crossing car is still moving across (i.e. that it didn't stop in my lane).


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## NOGA$4ME (Sep 30, 2016)

This is a somewhat annoying behavior of TACC/AP...it doesn't consider a vehicle out of your lane until it's *100% out of your lane*. Particularly annoying when it's a slow moving car and your car has backed way off on the speed and increased the following distance to suit (more on this in a minute). So while there is plenty of speed to start accelerating back up to speed as the car exiting the lane is 50% or more out of the lane (and that is what a human would do, and that is what cars behind you are _expecting_ you to do), the car simply refuses to accelerate until the car ahead is completely out of your lane. Like others have mentioned, I usually press the accelerator myself. Auto lane change has a feature where it will accelerate before making the lane change in order to make a pass, even if it would creating a closing speed and distance in your current lane that is outside of "normal". It seems like this is a similar type of situation, except it's the car that's ahead of you making the change, and not you.

Now, as long as we are on the topic, one other complaint I have is that the following distance should be speed aware. A setting of "2" in the following distance should correspond to one distance when traveling 70mph, but a completely different distance when traveling at 5mph. We all learned this when we learned to drive. And I suppose it does do this to a certain point. But I normally have my following distance set to "1", and when stopped in traffic it leaves an enormous gap to the car ahead of me.


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## Ed Woodrick (May 26, 2018)

gary in NY said:


> I've noticed that when my car is following behind another while in AP or TACC, and that car slows and turns off, my car wants to almost come to a complete stop, sometimes hesitating or even making a false start to get back up to speed. This is even though the turning car has cleared the lane and moved on. This isn't so much an issue for me, but the cars behind me are anticipating that my car is going to react the way most normal cars do, so they prepare to speed back up. But I'm not moving as fast as they anticipate, which causes them the stop short, sound the horn, yell obsinities, etc.. In the worse case they could rear end my car. Of course they are following too closely if they hit me, but I'd rather not be in that situation at all.
> 
> This happened today when a F-150 was following me closely, and the car in front slowed to turn right onto a side road. AP nearly stopped, did a false start, then started back up again. The F-150, was nearly in my trunk after this. A short time later while in TACC, the car did basically the same thing. This time there was no car following me. I did not think to save the dashcam video in either case, but I will try the next time this happens.
> 
> ...


Bring follow distance back to three. (Max should only be used for long range, sparse, Interstate travel)
It's Beta, not perfect. 
Just add some foot to the accelerator when this happens and life is good.


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## MelindaV (Apr 2, 2016)

NOGA$4ME said:


> his is a somewhat annoying behavior of TACC/AP...it doesn't consider a vehicle out of your lane until it's *100% out of your lane*.


there was a teslacam recently (so no sound) of a car supposedly rear ending a truck changing lanes ahead of them. I doubted it was actually TACC/AP to blame because it is so cautious on passing a car that just changed lanes. IMO, I'd rather it be too cautious, and I can hit the accelerator when needed, than not cautious enough.


NOGA$4ME said:


> one other complaint I have is that the following distance should be speed aware. A setting of "2" in the following distance should correspond to one distance when traveling 70mph, but a completely different distance when traveling at 5mph.


it does vary the follow distance depending on speeds. I spend most of my commute in stop and go traffic and can assure you at 1 when under 5mph is totally different than at 1 at 60mph.


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## NOGA$4ME (Sep 30, 2016)

MelindaV said:


> there was a teslacam recently (so no sound) of a car supposedly rear ending a truck changing lanes ahead of them. I doubted it was actually TACC/AP to blame because it is so cautious on passing a car that just changed lanes. IMO, I'd rather it be too cautious, and I can hit the accelerator when needed, than not cautious enough.


Agree on the preference of it being too cautious, but I think it's being so overly cautious in this case that it potentially confuses drivers behind who are expecting different behavior. Granted, this may not be easily achievable as the object detection might be very black and white about the fact that an obstacle is either in your lane or an adjacent lane, not really a "75% into the next lane and increasing" type of result, but eventually I think that kind of functionality is needed.



MelindaV said:


> it does vary the follow distance depending on speeds. I spend most of my commute in stop and go traffic and can assure you at 1 when under 5mph is totally different than at 1 at 60mph.


Yes, it's different. Of course. But it's not different enough for my taste.


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## MelindaV (Apr 2, 2016)

NOGA$4ME said:


> Yes, it's different. Of course. But it's not different enough for my taste.


and from what it seems, it acts differently from day to day. Sometimes a 2 at 10mph will be different than how it is the next day. Not sure what other things impact how it decides on a follow distance, but it does seem like there is more to it than just the current speed.


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## iChris93 (Feb 3, 2017)

MelindaV said:


> and from what it seems, it acts differently from day to day. Sometimes a 2 at 10mph will be different than how it is the next day. Not sure what other things impact how it decides on a follow distance, but it does seem like there is more to it than just the current speed.


I wish we had a better understanding of this.


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## MJJ (Aug 7, 2016)

And then there’s the flip side, where you’ll be cruising along and someone will merge in front way too close (on my route, it’s usually a semi) and as long as they hold speed the Tesla will keep that spacing for much too long. “Where’s that itchy braking logic now?” I will shout at the screen, with my foot hovering nervously over the accelerator.

But yeah. You can tell, it knows to the inch when a car ahead has *left* the lane, even, as noted above, too far ahead. And it will wait until that moment to resume speed. So why can’t it know better when someone is coming in?


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## MelindaV (Apr 2, 2016)

MJJ said:


> I will shout at the screen, with my foot hovering nervously over the accelerator.


just roll the thumb button down a little to slow down (without disengaging AP), or to the left to increase the follow distance. driving in traffic, I am constantly changing the follow distance to accommodate whatever is going on around.


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## NOGA$4ME (Sep 30, 2016)

MJJ said:


> And then there's the flip side, where you'll be cruising along and someone will merge in front way too close (on my route, it's usually a semi) and as long as they hold speed the Tesla will keep that spacing for much too long. "Where's that itchy braking logic now?" I will shout at the screen, with my foot hovering nervously over the accelerator.


I guess it's starting to stray from the initial concern, but merge behavior has really come a long way. My experience with it now is that it usually behaves predictably and correctly, although it did slam on the brakes the other day to let a particularly slow merging vehicle in (there was plenty of merge lane left, but I suppose the cameras aren't really looking for that). Not sure what the _correct_ behavior should be there. Based on speed differential the car could make a go/no-go decision about whether it's going to allow the car to merge in front or pass it by, but you could make the argument that slowing down is safer in the event the car unpredictably starts to merge even though it's going way too slow and should have checked their mirrors.


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## gary in NY (Dec 2, 2018)

In my first example, the turning car had completely cleared the lane, and then some, onto the side street when the car did it's false start. That was the point where it could have simply returned to cursing speed. But it very noticeably slowed/braked for a moment, which was the same moment the vehicle behind assumed it was safe to resume cruising speed. The initial slow down/near stop for a turning car had a safety margin of about 200% of what reasonable driver would do. I've no problem with the overabundance of caution, so long as the cars behind are expecting/operating under the same parameters. Most human drivers here are quite the opposite. This is where the safety of my vehicle, and me personally, is compromised. I'm not so sure the following distance has anything to do with the false start. The turning car was out of the direction of travel after making the 90 degree turn onto the side road and proceeding. There was no oncoming traffic at this point.

In the second example of the car turning into a gas station, it can be argued that the car was still in the range of TACC, moving more or less parallel to my lane, but also about two lane widths away from my lane. Is this different from passing a slower car in the right hand lane of a four lane highway?

The coexistence of cautious autonomous self driving systems and average human drivers (subject to distraction, aggression, slow reactions, impaired abilities, etc.), is going to be an interesting one.


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## ltphoto (Jan 30, 2018)

This is still definitely beta SW and a work in progress. I just finished a three week, 6100 mile trip. Most of the time EAP and NOA was a help and made the trip much easier. It saved my bacon once when a van changed lanes right into me at 75mph. EAP swerved and braked instantly as the van passed just inches from my front quarter panel. I would never have been able to react as quickly and it would have been bad. Other times, however, EAP seemed to be completely confused. Twice it refused to pass large semis when I had a clear path. It just slowed down and stayed a little behind them. I just had to use the accelerator to cruise on by and then everything worked well again. NOA was more problematic. Many times it was satisfied with just sitting behind slow moving traffic when there was a clear passing lane. Other times it wanted to change lanes right into another vehicle right next to me. I ended up not using NOA very much since the error rate was so high. Overall thought, EAP was a big benefit on long trips and I'm glad to have it. Looking forward to it improving more in the future.


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## turnem (Apr 26, 2019)

I'm a little late to the party here but I was starting to post a new thread and the forum appropriately recommended I check out this one before posted.

I'm 100% in agreement with the OP. Even my wife, who is a super nervous driver, thinks that the stopping behavior of AP when a car is turning out of your lane ahead of you is FAR too conservative. And as noted, I'm always concerned that I'll get rear-ended. So I keep my foot on the accelerator to babysit AP.

I've played with the follow distance settings quite a bit and it makes no difference for me. I'm usually on 1 or 2 in the city and I increase it to 3 on the interstate or faster moving main roads in town.

I'm assuming they have plans to eventually read blinkers and tail lights right? If so, this could help a lot with the logic in this situation. When it sees a blinker it can begin slowing ever so slightly to INCREASE the follow distance while waiting on the car to get out of the way without coming to a complete stop and then resume once the car is out of the way. I'm sure I've greatly over-simplified it. There are much smarter folks than me working on this but... just a thought.

I'll also echo the comments on the scenario when a car is crossing the street pretty far in front of you. The car breaks pretty hard and then sort of hesitates before resuming. I get why it does this and I'm glad that it prioritizes safety above all else. But hopefully they can continue to refine this sort of behavior to make it more human like.

On a very positive note - I was blown away on my morning commute this morning with how the car handled a lane change on a particularly curvy portion of the road. The road was sharply turning to the right (slow traffic - roughly 15 mph) and I was in the right hand lane and wanted to get into the left hand lane. I put on my blinker and expected the car to bounce me left and then quickly turn sharply back to the right to stay in the lane while turning. However, it took a straight line into the lane change and continued smoothly turning with the road. It was VERY human like and impressive.


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## NOGA$4ME (Sep 30, 2016)

I watched the Tesla Autonomy Day presentation, and I have a new appreciation for the types of things that the neural nets are looking for, particularly the "cut in" (and I hope "cut out") behavior. This is really impressive, and speaks to how the car has improved with merging behavior. Whether intentional or not, I would presume that the neural net would "learn" that blinkers (and brake lights) do affect the probabilities of cut-ins (and cut-outs).

I do wonder though, despite Elon's continued trashing of LIDAR for self-driving, if this conservatism does show a weakness of the vision system: inability to precisely position the car moving out of your lane in 3D space. Granted, I would expect the vision system to eventually "get there", and I don't disagree with cutting costs by avoiding adding a LIDAR system to the vehicle, but I think Elon is way too caught up on LIDAR-only vs. Vision-only. Cost issues aside, it seems like a solution that used both would be technically superior than one or the other.


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## turnem (Apr 26, 2019)

NOGA$4ME said:


> I watched the Tesla Autonomy Day presentation, and I have a new appreciation for the types of things that the neural nets are looking for, particularly the "cut in" (and I hope "cut out") behavior. This is really impressive, and speaks to how the car has improved with merging behavior. Whether intentional or not, I would presume that the neural net would "learn" that blinkers (and brake lights) do affect the probabilities of cut-ins (and cut-outs).
> 
> I do wonder though, despite Elon's continued trashing of LIDAR for self-driving, if this conservatism does show a weakness of the vision system: inability to precisely position the car moving out of your lane in 3D space. Granted, I would expect the vision system to eventually "get there", and I don't disagree with cutting costs by avoiding adding a LIDAR system to the vehicle, but I think Elon is way too caught up on LIDAR-only vs. Vision-only. Cost issues aside, it seems like a solution that used both would be technically superior than one or the other.


I think it's one of those situations where he has dug his heels in on LIDAR and its become a little bit of a bur in his saddle.


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