Model X

Autopilot braking hard at bridges

edited November -1 in Model X
We are 5200 miles into a 7500mile road trip around the US, and just twice we have encountered sever braking from autopilot. On each occasion it was on a straight piece of interstate, I10 westbound, and I40 eastbound, and in both cases, the sun was ahead of us casting a very dark shadow of the bridge onto the road. The braking was so severe - i.e dropping 25 to 30mph as fast as it possibly could, that I am fairly sure that if the motorcyclist who was following me had not turned off at the previous exit, he would have run right up my trunk on I40. Is this a common problem? For the rest of the trip I will be leaving AP whenever I see a bridge, then turning it back on afterwards.

On a less important note, on both of the Interstates mentioned, there are very long stretches that are dead straight, and although I hold the steering wheel with both hands at 10 to 2, quarter to 3, or 20 to 4, I get the flashing white reminders at regular intervals. It would be good to see an upgrade that extends the interval between warnings for dead straight roads... just a thought!


  • edited May 2018
    Severe not sever...
  • edited May 2018
    Same here. Driving at approx. 9pm (i.e. no sun) on freeway yesterday evening with TACC, car suddenly brakes under bridge. Not the first time it happened, and not only when using AP.
  • edited November -1
    For the straight sections, holding wheel with one hand, letting the weight of your arm provide a continuous pressure on the wheel keeps autopilot happy while at the same time giving you a feel for what it is doing, keeping you more connected to the road.
  • edited May 2018
    Never had this happen, and I have specifically worried about this when I see very dark shadows like bridges or barriers. Mine is fine.
  • edited November -1
    When commenting on exhibited Autopilot behavior(s), it's essential to provide the car's firmware version...

  • edited May 2018
    @ mathwhiz: correct, forgot to mention that. It's 2018.14.2
  • edited May 2018
    ...and the AP version. My X has AP1 and this has never happened BUT my loaner the other day had it happen numerous times in the same day. The loaner was on AP2. The common 5hread was the sunny day and dark shadows. can thank the nanny nag on the dummies who were bragging about the stupid things they were doing while on AP1 when it first came out. Not likely they will change it or lessen the nag times in the near future.
  • edited May 2018
    @alanduxbury. I used to get this often last year - going under a bridge caused both the hard braking and sometimes a swerve (just to keep my on my toes).

    When I got 2018.10 earlier this year, it stopped happening under bridges, although it still happens periodically at other places - like on the motorway or highways with no traffic in front. It's a great way to scare me, my passengers and the cars behind!

    I still reflexively grab the wheel just a little bit harder and raise my foot to the accelerator whenever I go under a bridge.
  • edited May 2018
    Sorry I forgot the version number, 2018.12.
  • edited July 2018
    Just got my M3 this month and went on a 1,900 mile road trip.

    Awesome car, HOWEVER, experienced three hard braking incidents approaching overpasses on interstate. Scared me as well as I think, several other motorists in close by vehicles. Hope Tesla fixes that pretty quick before an accident results from this. Version 2018.24.8
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