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Has TACC given you a bad scare?

Discussion in 'Model S: Driving Dynamics' started by AB4EJ, May 16, 2016.

  1. AB4EJ

    AB4EJ Member

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    Being a new Model S owner, I am still familiarizing myself with everything, and have been using TACC whenever possible. This works well for traffic that is moving at a fairly constant rate, or is stop-and-go. However on two separate occasions, I have had to do a hard panic stop to avoid running into the back of a stopped car. Here is the scenario:

    I am going along fine using TACC, and the MS stays behind the next car well - that is, it keeps the distance I have set, slows down (and stops) when the car in front of me stops, and speeds up appropriately. However - after I have followed another car (which moved to another lane), the MS now speeds up to the set cruising speed. Going 55 mph, now I approach a car stopped in my lane (at traffic signal). The MS does not slow down at all, and I have to jam on the brakes to avoid rear-ending the stopped car.
    • Is this normal behavior? (i.e., I am supposed to manage stopping for stopped vehicles myself, and not depend on TACC to do it)
    • Is there something wrong with the way my car is working, or have I done something wrong?
    By way of background, Autopilot was disengaged during this; weather has been clear and it is daytime. The main reason I thought TACC should be able to handle this situation, was that when I did my test drive in Atlanta, I was directed to try using TACC in traffic, and it stopped like it should. Can someone explain?
     
  2. chillaban

    chillaban Member

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    The behavior you noted is normal and is called out in the manual. The front radar sensor works on a combination of pulsed modulation and FM Doppler principles. It can only identify a car by the fact that it's a large radar signature that was moving. Otherwise to the radar it looks identical to the road, overhead street signs, trees, and other non-moving objects.

    A clever enhancement on this ability is that if the radar observes a once moving object that stops, it still remembers that the stopped object is a car.


    So this leads to a dangerous scenario: if you are following a car that suddenly moved out of the way to expose a stopped car, the radar sensor will not recognize the stopped car! The camera may be able to recognize the car especially at very slow speeds but it has almost no depth perception.

    The manual specifically states that above 50mph, this situation is particularly dangerous. It's something everyone needs to watch out for. Always check the instrument cluster and verify if it sees a car in front of you, especially if another car just got out of the way.
     
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  3. jeffro01

    jeffro01 Active Member

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    Indeed, this is something I have to pay close attention to in traffic here in CA. The stopped lane that I can't see until the car in front of me darts out of the lane to expose it... To date, the car has successfully picked up the stopped traffic, and acted accordingly, 70%'ish of the time which isn't close enough for me to "trust" that TACC will properly handle this situation all of the time.

    Jeff
     
  4. ecarfan

    ecarfan Well-Known Member

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    As @chilliban points out, this is a known limitation of TACC.

    I would also note that Tesla recommends as a general rule to only use AutoPilot functions when on freeways or highways without cross traffic. You stated there was a traffic signal on the road you were on, indicating cross traffic.
     
  5. AB4EJ

    AB4EJ Member

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    Excellent - thanks for the feedback. User error. I understand now that the radar can't tell between the stopped target and the background clutter. Good thing I was alert enough to take action.
     
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  6. Saghost

    Saghost Active Member

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    As the others have said, stopped cars are an issue right now.

    I expect Tesla will eventually improve the situation, probably leveraging the camera's object recognition in fusion with the radar - if they ever fix potholes and road debris it'll be this way, and any such update would solve the stopped cars at the same time.
     
  7. cman8

    cman8 Member

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    Also, Doesnt it say in the manual not to use where theres traffic lights? Not sure just wondering I thought I read it somewhere
     
  8. mkjayakumar

    mkjayakumar Active Member

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    There is another but similar scenario that I often encounter that bothers me: Your are cruising down the freeway at 65, no one in front of you for about 1/8th (or sometimes quarter mile) and there is a stopped car in front (often happens at lane drops and construction areas). I can clearly see the stopped car at a distance and the camera has not picked it up yet, There is still some distance, so I am not worried.

    And then a bit closer the camera picks it up, but car is still blissfully going at 65.

    About half the time the radars detect the stopped car and slow down (a bit too close to my liking) and come to a stop. That makes me very nervous. At other times, it gets too close and I am not sure if it is ever going to detect at all, and so I slam the brakes and stop it.
     
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  9. ecarfan

    ecarfan Well-Known Member

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    As several people have pointed out in this thread, TACC will not reliably identify objects that are not moving. This is a known limitation, and Tesla is clear about it.
     
  10. chillaban

    chillaban Member

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    Another good example of this is cresting a hill and encountering stopped cars.

    I think it's great that the Tesla instrument cluster draws what the car thinks it's seeing. It makes it a lot easier to decide well in advance whether or not the car is going to behave correctly before you are forced to take emergency corrective action and scare the crap out of your passengers.
     
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  11. AB4EJ

    AB4EJ Member

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    I guess we're discussing something that has already been discussed. But I must say, the fact that the radar allows you to come up on a stopped vehicle with a high closing speed and it doesn't even sound a collision warning... it makes me wonder if the collision avoidance system is working as we would wish.

    That said, it may be that we are asking more of the current suite of sensors than they can really provide, and new hardware might be needed to handle this situation.... which would certainly have to work for an autonomous vehicle.
     
  12. S4WRXTTCS

    S4WRXTTCS Active Member

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    I tend to be pretty vigilant with TACC so I haven't had any major scare with it.

    I don't use it on roads with a lot of traffic and red lights.
    I tend to use higher settings (3-5) to give me more time to react
    I tend to take over quickly when someone quickly cuts in or cases where the person in front of me exits and there is another car right in front of him

    My feeling is that we really need the tricamera solution to have a more worry free autopilot/tacc.

    Keep in mind that this TACC is WAY, WAY better than old school adaptive cruise control other cars had years ago (and some still do today). In those cars they would suddenly brake if there was a curve in the road and they mistook the car next to you for being in front of you.
     
  13. brec

    brec Member

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    The strings "traffic light" and "traffic signal" do not appear in the Owner's Manual.
     
  14. David29

    David29 Member

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    On the other hand...I have had experiences in which TACC flashes the red warning and sounds the alarm when it thinks it detects an object in my path, but there is none. One case occurred yesterday. I was on a curve, and I think the TACC detected a parked car (not in my travel lane). Although this is startling, at least it is erring on the side of caution.
     
  15. davidc18

    davidc18 Member

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    TACC is much improved since its rollout.
     
  16. wdolson

    wdolson Active Member

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    I read someone got into an accident on I-5 in California about a week ago in that very scenario. The three camera layout on the new AP coming soon will probably do a better job detecting stopped cars in front of you.
     
  17. Screwbal

    Screwbal Member

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    I've been afraid of this scenario so I'm quick to lower the AP speed when anything gets congested if traffic is slowing down and I feel it needs it.

    Because for this example on a freeway where it's 70 when we crawl to bumper <-> bumper I drop it to the lowest 18 mph. It makes me feel if it loses the car ahead it won't launch so hard and buy me/it more time.
     
  18. mkjayakumar

    mkjayakumar Active Member

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    I do that too ...
     

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