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The dangers of TACC with Speed Assist

arbr2

Member
Sep 21, 2019
30
38
The Netherlands
Dramatic title, I know. But it’s a fair one: TACC with Speed Assist on Model 3 in its current form can be outright dangerous. I’ve seen more people complain about this for more than a year now, but now that I’ve experienced it myself I really feel it should either be fixed or disabled right away for Model 3.

Make no mistake: I love my Model 3 and am extremely impressed with it. It’s simply the best car I’ve ever owned, nothing comes close. TACC with Speed Assist seems to be one of the few major design flaws of the vehicle.

Here’s an example that actually happened to me. It might seem like an edge case, but it isn’t. It’s a very common situation and will be encountered by many drivers on a daily basis.


Tesla Model 3 Performance
Software 2019.32.2.1 9b8d6cd


Expected and safe behaviour
Germany, Autobahn A3, Speed Limit: none
Speed Assist presets TACC to 150 kmh
On TACC engagement, M3 will try to accelerate to and maintain 150 kmh

Unexpected and dangerous behaviour
Germany, Autobahn A3, Speed Limit: none, Temporary Speed Limit: 80 kmh
Speed Assist presets TACC to 150 kmh
On TACC engagement, M3 will try to accelerate to and maintain 150 kmh

Drivers will not expect the sudden and unintended acceleration resulting in possible dangerous situations. Even if drivers are aware, cruise control is effectively rendered useless in these situations.

The main design flaw is that the driver cannot set TACC to the current speed. It will always preset speed to what Speed Assist thinks is the current speed limit (plus/minus offset), this behaviour cannot be overridden. It is impossible for the driver to select current speed, nor is it possible for the driver to overrule the set speed by Speed Assist before TACC is engaged. This would be reasonable behaviour if Speed Assist would recognise the actual speed limit. However, all speed information is currently based on a database. This data is often outdated or incorrect for many roads, does not take into account time of day nor any temporary restrictions.

The only way to operate TACC with SA would be to engage TACC at 150 kmh, but keep the current speed by keeping the accelerator depressed. Only then can the speed be reduced by turning the right scroll wheel. However, reducing the set speed from 150 to 80 kmh takes 14 ‘fast scrolls’. Furthermore, once TACC is disabled and re-enabled, the speed will be set back to 150 kmh, requiring the same procedure again to safely use TACC.

Model S/X does have a very simply way to set the current speed, even with Speed Assist enabled. This is how it should work on Model 3, there is absolutely no reason to have the current design in production vehicles on public roads. It’s a dangerous feature that can result in unexpected behaviour at high speeds.

I have already filed a report with Tesla. This thread is mainly meant to attract as much attention from Tesla and other Model 3 drivers as possible, this needs to be fixed. A fix should be relatively simple: make it possible for the driver to overrule Speed Assist before TACC engagement and/or enable a way to set TACC to the current speed.

Please feel free to share your experiences. Am I missing something? Is there a magic hidden way to overrule Speed Assist with TACC?



TL/DR

SpeedAssist presets speed for TACC based on incorrect speed limits. The driver cannot overrule this prior to TACC engagement, possibly resulting in unexpected acceleration, speeding fines or serious accidents. This behaviour is dangerous and should be fixed as soon as possible.
 

Az_Rael

Supporting Member
Supporting Member
Jan 26, 2016
5,653
8,941
Palmdale, CA
Agreed, it sucks. Imagine what it was like before the scroll wheel could control your speed - you had to madly tap on the screen to lower the set speed. Super dangerous.

Best workaround I have heard is to set speed assist to the max negative it can go. Then if the speed limit is higher, you can manually accelerate up to speed and engage. My other trick is to get up behind someone going slow then engage TACC, then reduce speed on the wheel as needed.
 

arbr2

Member
Sep 21, 2019
30
38
The Netherlands
Best workaround I have heard is to set speed assist to the max negative it can go. Then if the speed limit is higher, you can manually accelerate up to speed and engage.

I have seen this workaround posted before, but I don't understand how this would work?
The max offset is -/+ 10 km/h. So even with -10 offset, the speed would still set to 140 where 80 is allowed.

The quickest fix would simply be a toggle to disable Speed Assist. After SA is improved and safe, it can be turned back on by the driver.
 

David29

Supporting Member
Supporting Member
Aug 1, 2015
2,268
1,961
DEDHAM, MA
Dramatic title, I know. But it’s a fair one: TACC with Speed Assist on Model 3 in its current form can be outright dangerous. I’ve seen more people complain about this for more than a year now, but now that I’ve experienced it myself I really feel it should either be fixed or disabled right away for Model 3.

Make no mistake: I love my Model 3 and am extremely impressed with it. It’s simply the best car I’ve ever owned, nothing comes close. TACC with Speed Assist seems to be one of the few major design flaws of the vehicle.

Here’s an example that actually happened to me. It might seem like an edge case, but it isn’t. It’s a very common situation and will be encountered by many drivers on a daily basis.


Tesla Model 3 Performance
Software 2019.32.2.1 9b8d6cd


Expected and safe behaviour
Germany, Autobahn A3, Speed Limit: none
Speed Assist presets TACC to 150 kmh
On TACC engagement, M3 will try to accelerate to and maintain 150 kmh

Unexpected and dangerous behaviour
Germany, Autobahn A3, Speed Limit: none, Temporary Speed Limit: 80 kmh
Speed Assist presets TACC to 150 kmh
On TACC engagement, M3 will try to accelerate to and maintain 150 kmh

Drivers will not expect the sudden and unintended acceleration resulting in possible dangerous situations. Even if drivers are aware, cruise control is effectively rendered useless in these situations.

The main design flaw is that the driver cannot set TACC to the current speed. It will always preset speed to what Speed Assist thinks is the current speed limit (plus/minus offset), this behaviour cannot be overridden. It is impossible for the driver to select current speed, nor is it possible for the driver to overrule the set speed by Speed Assist before TACC is engaged. This would be reasonable behaviour if Speed Assist would recognise the actual speed limit. However, all speed information is currently based on a database. This data is often outdated or incorrect for many roads, does not take into account time of day nor any temporary restrictions.

The only way to operate TACC with SA would be to engage TACC at 150 kmh, but keep the current speed by keeping the accelerator depressed. Only then can the speed be reduced by turning the right scroll wheel. However, reducing the set speed from 150 to 80 kmh takes 14 ‘fast scrolls’. Furthermore, once TACC is disabled and re-enabled, the speed will be set back to 150 kmh, requiring the same procedure again to safely use TACC.

Model S/X does have a very simply way to set the current speed, even with Speed Assist enabled. This is how it should work on Model 3, there is absolutely no reason to have the current design in production vehicles on public roads. It’s a dangerous feature that can result in unexpected behaviour at high speeds.

I have already filed a report with Tesla. This thread is mainly meant to attract as much attention from Tesla and other Model 3 drivers as possible, this needs to be fixed. A fix should be relatively simple: make it possible for the driver to overrule Speed Assist before TACC engagement and/or enable a way to set TACC to the current speed.

Please feel free to share your experiences. Am I missing something? Is there a magic hidden way to overrule Speed Assist with TACC?



TL/DR

SpeedAssist presets speed for TACC based on incorrect speed limits. The driver cannot overrule this prior to TACC engagement, possibly resulting in unexpected acceleration, speeding fines or serious accidents. This behaviour is dangerous and should be fixed as soon as possible.

Wow, I had not realized that Model 3 lacks the ability to set TACC to the current speed. As a Model S driver, I can do that easily. And what helped me at first, is that the cruise control levers and logic were both identical to the Mercedes Benz cars I had earlier, so i simply continued my familiar behavior. Not that my "vote" counts at all, but I agree that is a serious flaw in the Model 3 controls....
 

Az_Rael

Supporting Member
Supporting Member
Jan 26, 2016
5,653
8,941
Palmdale, CA
Or you could turn off TACC and manage the speed yourself. :-O

Eh, I paid $5k for the privilege, I am gonna use TACC.


I have seen this workaround posted before, but I don't understand how this would work?
The max offset is -/+ 10 km/h. So even with -10 offset, the speed would still set to 140 where 80 is allowed.

The quickest fix would simply be a toggle to disable Speed Assist. After SA is improved and safe, it can be turned back on by the driver.

Ah, didnt know how low speed assist would let you go when set to metric. Here in the US, the minus amount is usually sufficient to account for wrong speed limit data.


I would love for the default to be set speed to driving speed. That would solve a lot of issues. Maybe only the double click for AP could get you the speed assist stuff.
 
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arbr2

Member
Sep 21, 2019
30
38
The Netherlands
I've looked around on TMC, but I couldn't really find a 'wish list' or a 'this needs fixing' list on here. As we're all running into similar issues, wouldn't it be nice to have some sort of unified thread where issues are listed by priority? Maybe using a voting system to determine priority within the community.

I can't image Tesla staff scouring all the forums and incoming flood of emails. While they might have an idea of what its drivers want, a list based on votes might make selecting the issues to fix that much easier. Or in the very least make the community feel heard and make it easy for members of the community to see if an issue is already on the list.

It clearly seems that stuff like the 'rain sensor' issues and these TACC/SpeedAssist related issues are high on the list of almost any Model 3 driver. There's probably a couple more of these issues that would improve daily use of a Model 3 for virtually all it's customers.
 

XLR82XS

D M C
Jul 26, 2019
3,153
1,954
SWFL | Vegas
Eh, I paid $5k for the privilege, I am gonna use TACC.

I would love for the default to be set speed to driving speed. That would solve a lot of issues. Maybe only the double click for AP could get you the speed assist stuff.
I paid $0 - included with my LR premium. I'm not having TACC speed set issues. When I engage it sets at the speed travelling. I do see AP automatically slow down in certain residential streets/low speed limit roads and providing a warning stating "autopilot limited to xxmph"
 
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arbr2

Member
Sep 21, 2019
30
38
The Netherlands
I'm not having TACC speed set issues. When I engage it sets at the speed travelling. I do see AP automatically slow down in certain residential streets/low speed limit roads and providing a warning stating "autopilot limited to xxmph"

Interesting, what software version are you on?

And could it be that you're always going over the speed limit, because in that case it will indeed set the speed to the current speed ;) In any other situation the TACC speed will be set to speed limt +/- offset, not the current speed your driving at.
 

SSonnentag

Let’s go Brandon!
Apr 11, 2017
1,748
2,351
Arizona
Is the Model 3 like the S and X where if you set TACC and the car starts accelerating, you can press the accelerator pedal slightly and "throttle" control switches over to manual instead of whatever acceleration curve TACC uses?
 
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DopeGhoti

Active Member
Aug 28, 2019
1,242
1,429
Phoenix, AZ
Is the Model 3 like the S and X where if you set TACC and the car starts accelerating, you can press the accelerator pedal slightly and "throttle" control switches over to manual instead of whatever acceleration curve TACC uses?
In part, no. If you actuate the accelerator beyond the point where TACC is telling the car to accelerate, you will override TACC and go faster. Eventually, TACC will pop up an advisory on the screen that TACC will not brake while you are so overriding it. When you release the accelerator, TACC will resume control at the speed at which it was set (or, if you adjusted its settings while overriding it, at the speed to which you had set it). The only pedal that disables TACC is the brake.
 

mswlogo

Well-Known Member
Aug 27, 2018
6,154
5,316
MA, NH
Set your Speed Limit Offset to -20 mph (most negative value not sure what that is in kmh).

It will then always set TACC to your current speed.

This will greatly reduce phantom braking due to erroneous speeds the Tesla picks up via GPS maps.
 
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M3BlueGeorgia

Active Member
Dec 10, 2018
1,400
1,283
Atlanta, GA
The core complaint here is that the car doesn't know the actual speed limit, just the speed limit in its database.
Currently the software doesn't understand temporary speed limits.

As a result, you have to spin down the max speed setting. Fortunately it is quick to do that.

In the States there are time-of-day speed restrictions around schools, and the driver has to manually reduce the maximum speed, sometimes by 20mph, when passing through school zones when kids are arriving or leaving school.
We also have the same issue as you when going through construction zones.
 

arbr2

Member
Sep 21, 2019
30
38
The Netherlands
I'm usually at or slighter above the posted limit.

I am too, the problem is that TACC often does not adhere to the posted limit, because it simply has the wrong information.

Exactly as M3BlueGeorgia notes:

The core complaint here is that the car doesn't know the actual speed limit, just the speed limit in its database.
Currently the software doesn't understand temporary speed limits.

As a result, you have to spin down the max speed setting. Fortunately it is quick to do that.

It might be quick if you need to spin down from 70 to 55 mph, but take my original example of 150 km/h to 80 km/h. That's 14 spins, all while the car is already accelerating. And if TACC is disabled and re-enabled you have to do it all over again.
 

arbr2

Member
Sep 21, 2019
30
38
The Netherlands
Set your Speed Limit Offset to -20 mph (most negative value not sure what that is in kmh).

I agree this is a workaround, but the basic design is just poor and potentially dangerous.

By the way: the maximum offset is 10 km/h in Europe. That's just over 6 mph. Still, 20 mph (32 km/h) won't really help if the vehicle thinks you can do 150 km/h while 80 is actually allowed.
 

arbr2

Member
Sep 21, 2019
30
38
The Netherlands
maybe we can Twitter Brigade Elon into adding something like long-hold of the TACC stalk to enable TACC at the current speed?

I've thought about a couple of solutions as well, and this one is top of my list as well as it's probably the most elegant and best long-term solution.

Once Autopilot is able to properly read actual speed signs, SpeedAssist will probably be the best and preferred way of using TACC. The whole concept of driving at the speed limit where possible is excellent, as long as the perceived speed limit is correct. The driver should always be able to override SpeedAssist before enaging TACC.

A long-hold is a very specific input by the driver with clear intention of an override of default systems behaviour. It also doesn't conflict or confuse any other current operation of the stalk.
 
Last edited:
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