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Autopilot Doesn't Slow When Speed Limit Changes

Discussion in 'Model 3: Driving Dynamics' started by PianoAl, Jan 7, 2020.

  1. PianoAl

    PianoAl Member

    Joined:
    Dec 15, 2019
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    Location:
    Far Northern California
    I was surprised to find that when I went from a 65 MPH zone to a 50 MPH zone, the car didn't slow down. Maybe it would have later, but I didn't want to get a ticket.

    Is that the normal behavior as of now?
     
  2. M3BlueGeorgia

    M3BlueGeorgia Active Member

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    Dec 10, 2018
    Messages:
    1,286
    Location:
    Atlanta, GA
    Yes, that is the normal behavior.

    There are a few edge cases where the car will reset to the speed limit, but normally it doesn't.

    Tesla will have to fix this, and read speed limit signs, and support temporary and time-of-day speed limits before they can claim full self driving, but I haven't seen any chatter about when that software capability will be tested and/or released.
     
  3. JulienW

    JulienW Active Member

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    Atlanta
    It depends on the road. On a divide/limited access it wont' but in more urban single lane roads it will slow to 5MPH over the speed limit as the max speed on AP.
     
  4. M3BlueGeorgia

    M3BlueGeorgia Active Member

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    That's one of the edge cases.

    However, that logic uses the internal database of speed limits, which has an unacceptably high error rate. Unfortunately the car (since HW2) doesn't currently attempt to read speed limit signs (believed to be an IP issue, more than a software issue).

    The software also doesn't take account of temporary speed limits, such as in construction zones, or variable speed limits. It also doesn't take account of time-of-day speed limits, such as in school zones.
     
  5. mreynolds767

    mreynolds767 Member

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    Location:
    Boston
    Yes as Julien states on single lane back roads it does slow. Annoyingly so on some roads that have small sections rated way too low (in my opinion). Like those small sections where a 35 drops to a 20.
    But AP is not intended for use on these type of streets yet so cannot blame Tesla for that.

    Also, if on a highway and the highway changes name it will also slow the car. Happens to me everyday, one highway technically ends merges into another one but in practice you just stay in the left 3 lanes to go one highway and right 3 lanes for another so traffic does not slow.
    When there is no traffic 75 I would say is a common AP setting I might use.
    If in AP the car goes down to 55 here.
    The speed limit I know is 55. Not positive if before the divide the speed limit is 55, 60 or 65.
    I changed my settings so the relative speed limit is at +18 and that changed it to slow to 65 ; which is still not what I want but at least won't cause an accident. Without that adjustment, the sudden slow down to 55 was dangerous. Since I set to +18 though, should slow me down to 73.

    But otherwise, normal highway and the road changes speed limits, no the car will not change
    However if you go into your settings and change the auto pilot speed limit to absolute instead of relative and use that, then the speed should adjust each time the speed limit changes on the highway. I have not tried that since I don't want the car doing that without my control but something you may want to experiment with.
    Anything temporarily like a construction zone it will not read the lower limit though so no matter what the driver is responsible for knowing the speed at least currently.
     
  6. CharleyBC

    CharleyBC Active Member

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    Talent, OR
    Yeah, I’ve wished for this too. There’s a stretch of CA-16 we drive frequently (a rural 2-lane road) where the speed limit changes from 65 to 55 as it crosses the county line. The database is fine—the car knows both speed limits and displays them correctly. But the setting won’t change from 65 to 55 automatically. I just remember (usually) to touch the “55” sign on the screen, and that does it.

    I know some have argued against an automatic speed setting change, though I forget what their argument was. The solution is a config option on the Autopilot screen: “Change set speed to follow posted limits” On/Off. then everyone can have what they prefer.
     
  7. noicepls

    noicepls Member

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    Location:
    Lambton County ON.
    In basic Autopilot (the one that consists of TACC and Autosteer), that behavior is normal when using TACC. But when using Autosteer, (which uses basic GPS navigation), my car does respond to speed limit changes, and will slow down when going from 65 down to 50. Tesla should fix this and make TACC respond to speed limit changes as it already does in Autosteer, considering that basic Autopilot includes TACC and Autosteer together.
     

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