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Sudden Large Increase in TACC Set Speed ?

Tam

Well-Known Member
Nov 25, 2012
9,235
7,923
Visalia, CA
...I’m surprised there aren’t more posts on this. I can’t believe I’m the only one this is happening to. And it’s such a bizarre behavior.

I don't think you are the only one who has experienced this bug. I think most likely, others just don't take time to post it.
 

rxlawdude

Active Member
Jul 10, 2015
2,957
2,064
Orange County, CA
I got curious enough drive through the same route and try to reproduce what happened, and I had no problem reproducing it two times in a row.

While driving in TACC at between 60-70mph, the set speed simply jumps up to 90mph right after the speed limit sign on the screen changes to 70mph. (Side note: there are no actual 70mph speed limit signs.) Doesn’t appear to matter whether or not I’m manually increasing the set speed with the scroll wheel like the first time it happened. I tried it once each way.

I took a video and here are before/after screenshots taken a fraction of a second before and after the set speed jumps up to 90mph. The full video is at th bottom, and the jump happens at the 14-second mark.

Before: 65mph set speed.
View attachment 682437

0.1 seconds later: 90mph set speed.
View attachment 682438


WTF.
I don't see any cues visually that the car should interpret as a speed limit, so this must be a mapping bug, very specific to that location.

Defnitely a bug that should be reported and squished.
 

FloridaJohn

Member
Apr 1, 2016
368
445
Palm Beach Gardens, FL
It just happened again, but this time on a different interchange: driving from Northbound I-355 onto Westbound I-88 (in the western Chicago burbs).

TACC set speed was ~65mph going through the interchange. Then near the end of the ramp it jumped to 90mph.

I’m surprised there aren’t more posts on this. I can’t believe I’m the only one this is happening to. And it’s such a bizarre behavior.
I have experienced something similar when letting AutoPilot drive between two interstate highways.

When you are on the original highway, the car is going your set speed (presumable speed limit plus offset). Then, when you move from the highway to the off ramp, the car has a database with the speed for that off ramp. The car will slow to that speed. For me, it has always been lower than the main highway, but I don't know if that is universal.

Since this is an interchange between two highways, the off ramp becomes an on ramp for the second highway. As you get close to the merge point, the car either reads a new speed limit sign or pulls from it's database the speed for the second highway. The car will then accelerate up to the new speed limit plus your offset.

If this is what is happening to you, then the car is just slowing down for the transition between the highways. I know that some transitions do not have sharp turns and the highway may not visually look different, so cars may travel at the same speed between the highways. But the car thinks it should be slowing down, so it does.

Not sure if this is exactly what you are seeing, but I have experienced it at just about every transition between highways I can remember.
 

jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
I have experienced something similar when letting AutoPilot drive between two interstate highways.

When you are on the original highway, the car is going your set speed (presumable speed limit plus offset). Then, when you move from the highway to the off ramp, the car has a database with the speed for that off ramp. The car will slow to that speed. For me, it has always been lower than the main highway, but I don't know if that is universal.

Since this is an interchange between two highways, the off ramp becomes an on ramp for the second highway. As you get close to the merge point, the car either reads a new speed limit sign or pulls from it's database the speed for the second highway. The car will then accelerate up to the new speed limit plus your offset.

If this is what is happening to you, then the car is just slowing down for the transition between the highways. I know that some transitions do not have sharp turns and the highway may not visually look different, so cars may travel at the same speed between the highways. But the car thinks it should be slowing down, so it does.

Not sure if this is exactly what you are seeing, but I have experienced it at just about every transition between highways I can remember.
That’s what I suspected at first, but there’s no slowdown at all on the interchange mentioned in the first post. (EB IL-56 onto EB I-88)

But even if there was, the car should never automatically increase the set speed to higher than it was before you entered the interchange. See the quotes from the owner's manual that I posted in post #2 of this thread that discuss this. (Also, I don't use an offset of the speed limit for setting my set speed anyway.)
 

jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
I took the Northbound I-355 onto Westbound I-88 interchange again. This time I drove through it with TACC engaged and made sure not to touch the scroll wheel at any point, and it still raised the set speed to 90mph at the end of the interchange.

Details:
I entered the interchange with the set speed at 65mph. The car lowered the set speed on its own, first to 60mph and then again to 55mph as it went through the curve. Then it raised it to 60mph. And then towards the end of the ramp it raised it to 90mph. :rolleyes:

Video (set speed jumps at 0:47) (sorry for the shakiness and orientation) :
 

jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
BTW, I did do an online chat with Tesla Customer Service about this last week.

They asked some surprisingly detailed questions, first by having me report my car's current odometer and range so they could verifying my identity and which car I was driving (even though I was already logged into my Tesla account).

Then they asked me to share precise geo-locations (via Google maps links) for the 2 locations where this occurred. And they also wanted precise dates and times that it occurred, which I was able to provide since I use TeslaFi.

They said they would pass on the information to their engineering folks to investigate. Hopefully they follow through to find the bug that's causing this and fix it.
 

rxlawdude

Active Member
Jul 10, 2015
2,957
2,064
Orange County, CA
I took the Northbound I-355 onto Westbound I-88 interchange again. This time I drove through it with TACC engaged and made sure not to touch the scroll wheel at any point, and it still raised the set speed to 90mph at the end of the interchange.

Details:
I entered the interchange with the set speed at 65mph. The car lowered the set speed on its own, first to 60mph and then again to 55mph as it went through the curve. Then it raised it to 60mph. And then towards the end of the ramp it raised it to 90mph. :rolleyes:

Video (set speed jumps at 0:47) (sorry for the shakiness and orientation) :
A couple of observations: your set speed is always 15-30mph higher than the speed limit throughout your video. What is your speed offset setting in TACC? Please show that setting concurrently with your video.

But to fully understand what's happening when you apparently set your speed 15-20mph higher than the speed limit before it changes to 30mph higher (by itself), set your offset to zero, then set the cruise when you enter the offramp to the speed limit (40mph), and repeat this experiment.
 
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jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
A couple of observations: your set speed is always 15-30mph higher than the speed limit throughout your video. What is your speed offset setting in TACC? Please show that setting concurrently with your video.

But to fully understand what's happening when you apparently set your speed 15-20mph higher than the speed limit before it changes to 30mph higher (by itself), set your offset to zero, then set the cruise when you enter the offramp to the speed limit (40mph), and repeat this experiment.

I’ve noted repeatedly in this thread that I don’t use a speed limit offset setting for the set speed. My set speed setting is to engage at the current vehicle speed. This behavior has nothing to do with speed limit offsets in the set speed settings.

Also, FYI: prior to the start of the video, and before entering the interchange, I had initially engaged TACC at a set speed of 65mph when the speed limit was 60mph. The speed limit sign on the screen later briefly disappears after entering the interchange (due to lack of nav system data, I suppose), but you can see that the set speed is still 65mph at the start of the video before the speed limit sign reappears as 40mph.
 
Last edited:

rxlawdude

Active Member
Jul 10, 2015
2,957
2,064
Orange County, CA
I’ve noted repeatedly in this thread that I don’t use a speed limit offset setting for the set speed. My set speed setting is to engage at the current vehicle speed. This behavior has nothing to do with speed limit offsets in the set speed settings.

Also, FYI: prior to the start of the video, and before entering the interchange, I had initially engaged TACC at a set speed of 65mph when the speed limit was 60mph. The speed limit sign on the screen later briefly disappears after entering the interchange (due to lack of nav system data, I suppose), but you can see that the set speed is still 65mph at the start of the video before the speed limit sign reappears as 40mph.
Well, hopefully Tesla gets to the bottom of that, as I agree it potentially could be dangerous.
 

jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
I just discovered that this behavior isn’t limited to limited-access expressway/highway interchanges. It also happens on regular ol’ on-ramps onto I-88 from city streets.

I just tried engaging TACC on the on-ramp at IL-31/Lincolnway St onto EB I-88 in North Aurora, IL. Just like in the other instances, the set speed jumps to 90mph on its own at the end of the ramp.

I’m on 2021.12.25.7 now.
 

jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
Some more updates, in case anyone is interested... (I still can't believe no one else has reported anything like this happening in their Tesla...)

I've since discovered that this behavior occurs on at least 3 different Chicago-area tollways: I-88, I-355, and I-294. I haven't observed it anywhere else yet, but I also haven't had a chance to deliberately test it on any of the other freeways in the area yet, so not ruling those out.

The interesting discoveries I've made recently include:
  1. This behavior does appear to be related to the speed limit of the road I'm merging onto. For example:
    I-88 and I-355 have 60-65 mph speed limits, and the set speed jumps to 90mph when merging onto those roads.
    But I-294 has a 55mph speed limit, and the set speed only jumps to 85mph, or +30mph over the speed limit. (I'll once again note here that I don't use a speed limit offset for my set speed in the vehicle settings. I have it set to engage at the current vehicle speed.)
  2. This behavior doesn't always occur at similar locations. By this I mean... in most cases the set speed jumps towards the end of an on-ramp, near where the solid lane line on the left side of the merging lane ends. But in some cases it happens much earlier. For example, at the WB I-88 on-ramp at Farnsworth in Aurora, IL, the set speed jumps up only 100ft or so after turning onto the ramp, which is ~1/4 mile before you actually merge onto I-88.
  3. It appears to occur not most, but not all, on-ramps on I-88.
And here's a map I marked up with all the locations where I've observed the set speed jumping (including the speed it jumps to), and a few where it does not jump (noted in green). If anyone else in the west burbs of Chicago wants to test out how their car behaves and report it, that'd be cool. :cool:

1628891785775.png
 
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jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
What is your speed offset setting in TACC?
I don’t use a speed limit offset setting for the set speed. My set speed setting is to engage at the current vehicle speed. This behavior has nothing to do with speed limit offsets in the set speed settings.

Turns out I was wrong about this bug not being related to the Autopilot Set Speed speed limit offset setting...

Even though I have the Set Speed setting toggled to engage at the current vehicle speed with no speed limit offset, my car is still using the "greyed-out"/disabled speed limit offset setting (which for some reason I had set to +30mph) and applying that offset to automatically change my set speed on almost every highway on-ramp that I take. (The speed limit offset value is still retained in the vehicle settings even after you toggle back to using current speed. You can still see it in the Autopilot settings menu -- it's just greyed out.)

I verified this by changing the speed limit offset setting to a bunch of different settings, and the set speed reliably jumps to whatever that offset speed is on the vast majority of on-ramps. This happens equally whether the offset is set to a MPH offset or a % offset, and it also happens whether I leave the offset setting engaged or toggle back to Current Speed.

So it's really like 2 bugs in one:
  1. It's automatically increasing the set speed in the middle of on-ramps, which it's not suppose to do. (Note that TACC/AP can automatically decrease the set speeds when driving through interchanges and then later increase it back to the original set speed, as described in the owner's manual. But it's not supposed to randomly increase speeds based on speed limit offsets on on-ramps.)
  2. It's using the speed limit offset setting, even though I have that disabled.
I do still wonder if this bug is somehow unique to my vehicle, or if this is a widespread bug that's just flying under the radar since it's unusual to engage TACC/AP on on-ramps.
 

rxlawdude

Active Member
Jul 10, 2015
2,957
2,064
Orange County, CA
Turns out I was wrong about this bug not being related to the Autopilot Set Speed speed limit offset setting...

Even though I have the Set Speed setting toggled to engage at the current vehicle speed with no speed limit offset, my car is still using the "greyed-out"/disabled speed limit offset setting (which for some reason I had set to +30mph) and applying that offset to automatically change my set speed on almost every highway on-ramp that I take. (The speed limit offset value is still retained in the vehicle settings even after you toggle back to using current speed. You can still see it in the Autopilot settings menu -- it's just greyed out.)

I verified this by changing the speed limit offset setting to a bunch of different settings, and the set speed reliably jumps to whatever that offset speed is on the vast majority of on-ramps. This happens equally whether the offset is set to a MPH offset or a % offset, and it also happens whether I leave the offset setting engaged or toggle back to Current Speed.

So it's really like 2 bugs in one:
  1. It's automatically increasing the set speed in the middle of on-ramps, which it's not suppose to do. (Note that TACC/AP can automatically decrease the set speeds when driving through interchanges and then later increase it back to the original set speed, as described in the owner's manual. But it's not supposed to randomly increase speeds based on speed limit offsets on on-ramps.)
  2. It's using the speed limit offset setting, even though I have that disabled.
I do still wonder if this bug is somehow unique to my vehicle, or if this is a widespread bug that's just flying under the radar since it's unusual to engage TACC/AP on on-ramps.
Try enabling the offset and setting it to zero, then disabling it?
 

helvio

E-TARDIS
Aug 11, 2020
448
606
Phoenixville, PA
I do still wonder if this bug is somehow unique to my vehicle, or if this is a widespread bug that's just flying under the radar since it's unusual to engage TACC/AP on on-ramps.
I would say not, all cars have the same software. I do engage TACC/AP a LOT on ramps. I think the unusual setting is a +30mph offset, I never heard of anyone setting it over 15mph.
 

jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
Try enabling the offset and setting it to zero, then disabling it?

Tried it. No difference. Still automatically changes set speed on on-ramps.

This did, however, allow me to observe that the car will also decrease the set speed if it's set higher than the offset. For example, after I changed the offset to zero and then disabled the offset by toggling back to "current speed", if I increase the set speed to 70mph on a ramp and then merge onto a 60mph highway, the set speed will drop from 70mph to 60mph at the end of the ramp.

I would say not, all cars have the same software. I do engage TACC/AP a LOT on ramps. I think the unusual setting is a +30mph offset, I never heard of anyone setting it over 15mph.

Since the behavior is the same regardless of the size of the offset, I have to think that if this behavior existed on all Teslas or even every Model 3, there would be a ton of threads on this, wouldn't there?

According to every description of TACC/AP/Set Speed/etc. that I can find in the manual, the car simply should not be behaving this way.
 

HalfNHalfT

Member
May 23, 2021
51
80
Raleigh, NC
So I also have set to current speed and found the same thing with the part about it ignoring that and using my greyed out speed offset! This is for sure a bug … was about to create a new post on this. I confirmed this by enabling speed offset and changing what it was then putting it back on set to current speed and could tell it would occasionally use whatever my greyed out speed offset was. Between this and the massive deceleration incidents TACC / AP is super busted for me at the moment. I am on software 2021.4.21.3
 
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