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Exit speed limit signs confusing AutoPilot?

ZaphodBx

Member
Apr 20, 2021
27
23
Colorado
I saw there were some older posts on this, but given this is my first week with my Tesla, and I assumed things would have improved, I'm amazed at how the car picks up nearly all of the exit speed limit signs and aggressively slows down from 75mps to 50mph. It was literally like every 1-2 exits, so pretty much non-stop. I'll grant it that the signs were pretty much right on the main highway, but they were yellow and said "exit", so I wouldn't think it would be that hard to figure out. Is the speed limit aware cruise just worthless, or is there something I'm missing? So far, I love it other than this issue.
 

Tam

Well-Known Member
Nov 25, 2012
10,100
9,190
Visalia, CA
I saw there were some older posts on this, but given this is my first week with my Tesla, and I assumed things would have improved, I'm amazed at how the car picks up nearly all of the exit speed limit signs and aggressively slows down from 75mps to 50mph. It was literally like every 1-2 exits, so pretty much non-stop. I'll grant it that the signs were pretty much right on the main highway, but they were yellow and said "exit", so I wouldn't think it would be that hard to figure out. Is the speed limit aware cruise just worthless, or is there something I'm missing? So far, I love it other than this issue.

Just to clarify, are you saying that your car slows down on the freeway because it mistakenly read the exit sign speed instead of the freeway speed?

For example, the freeway speed sign is 75 MPH and the exit sign says 50 MPH?

Would you please look at the instrument cluster and see what it reports the speed signpost icon as 75 MPH or 50 MPH?

If the instrument signpost icon says 75 MPH and the car slows down to 50 MPH, that would be a phantom brake and not an error in reading exit speed while not exiting.

If the instrument signpost icon says 50 MPH and the exit sign says 50 MPH, then that is an error in reading exit speed while not exiting. I don't think I've got such an error before since 2017 but I've only driven around California and Nevada only. The error in reading exit speed while not exiting might happen in other places that I didn't know just yet.
 

ZaphodBx

Member
Apr 20, 2021
27
23
Colorado
Yeah, it's actually reading the exit speed limit sign and setting the cruise to that. I have it set to 5 over the speed limit, so when it sees the 45mph exit speed limit sign, it shows 50mph on the instrument signpost, and slows down to 50.

It was most common when I was in the right lane, but it happened from the left lane once as well. It might just be something with that stretch of road, but that's the only highway driving I've had to do so far, and it was really frustrating (and dangerous)!

I have one of the new radar-less Model Ys, but I wouldn't think that radar would come into play for this.
 

Tam

Well-Known Member
Nov 25, 2012
10,100
9,190
Visalia, CA
Yeah, it's actually reading the exit speed limit sign and setting the cruise to that. I have it set to 5 over the speed limit, so when it sees the 45mph exit speed limit sign, it shows 50mph on the instrument signpost, and slows down to 50.

It was most common when I was in the right lane, but it happened from the left lane once as well. It might just be something with that stretch of road, but that's the only highway driving I've had to do so far, and it was really frustrating (and dangerous)!

I have one of the new radar-less Model Ys, but I wouldn't think that radar would come into play for this.

In that case, it's the vision problem unrelated to radar. Your case is similar to when the "traffic and stop sign control" feature was released to radar-equipped cars, there have been reports that while driving on freeways without traffic lights, the vision system would pick up traffic lights at exits or streets overhead and the car would erroneously respond accordingly as if those traffic lights were on the freeway instead. It's been much better now.

Until Tesla will address your case, I guess you just have to take note of which lanes could prevent such issues.
 

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