# Trouble setting cruise control to lower speed than previous session. Help!



## BW984 (Nov 30, 2018)

I’m not sure if this is a bug or a feature or just poor user knowledge; please enlighten me.

Let’s say I’m driving down the interstate and set the adaptive cruise to 70mph. I then deactivate ACC to exit the interstate onto a frontage road that has a speed limit of 50mph. The ACC speed limit is still set to 70mph and nothing I’ve tried will complete clear the ACC or lower the grey’d out max speed value. As a result once I’ve slowed down to 50mph and wish to reset the cruise control the car will rapidly accelerate back towards 70mph while I frantically reduce the speed on the steering wheel back to 50. 

What am I doing wrong and how do I fix this or is this how the car is supposed to behave?


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## FRC (Aug 4, 2018)

Check(under Driving tab, I think) to see where your TACC speed is preset. You can set as an absolute speed or set relative to speed limit. Sounds like yours is set to an absolute 70.


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## garsh (Apr 4, 2016)

BW984 said:


> ...onto a frontage road


I think the car might mistakenly believe you're still on the Interstate, at least as far as determining the current speed limit for TACC.


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## BW984 (Nov 30, 2018)

After re-reading the manual I think @garsh is correct in that the TACC is thinking the speed limit on the frontage road is say 65mph instead of the actual 50mph limit. Would setting the speed limit max from relative to absolute in the autopilot settings and then putting the absolute max speed in the settings menu at say 90mph allow the cruise control to act normally where it'll set itself at whatever speed you are currently traveling?

Edit: I believe the answer to my question is yes. I'll try the absolute speed limit max setting next time I find an excuse to drive.


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## BluestarE3 (Oct 12, 2017)

I had a similar problem with the basic cruise control (no EAP). It wants to resume at the previously set cruise speed instead of setting cruise to the current speed of the car. The owner's manual isn't very helpful since it only talks about TACC and not basic cruise. There must be a setting/option (as with traditional cars) to tell it you want to set the cruise speed rather than resume at the previous speed, but I haven't found it yet.


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## BW984 (Nov 30, 2018)

The problem appears to be the system combining speed limit warnings with TACC even though they should have nothing in common whatsoever. I found a long thread on this exact topic over on another model 3 forum. Similar Thread Other Forum. I submitted the following to Tesla tonight to officially voice my concerns over this safety issue.

Hello,
The current behavior of Traffic Aware Cruise Control (TACC) automatically setting the cruise speed to the GPS database speed limit, even if the car is traveling well below that speed, is dangerous as it results in unintended and rapid acceleration of the vehicle.

School zones have reduced speed limits during certain hours of day that will not be captured by the GPS database; construction zones will similarly have reduced speed limits from the GPS database value for that highway. Additionally there are many roads where the GPS database speed limit is wrong; the GPS speed limit is 20mph higher than the actual speed limit on the I-20 frontage road required to get to my house.

All three of these scenarios benefit from cruise control to prevent speeding; however the current TACC system actually creates acceleration well over the real speed limit when trying to activate it at the real speed limit. Trying to set the cruise while traveling at the real 45mph speed limit when the TACC activates at 65mph is a very disconcerting and jerky experience requiring premeditated rapid thumb wheel scrolling; this is unsafe and unreasonable for a cruise control system.

The TACC system needs to be updated to set the vehicle speed at the current speed of the vehicle when it is activated. If the driver would like to then set the cruise speed to the GPS speed limit (+/- their customized offset) they should then tap the speed limit sign on the screen. A traditional "resume" functionality where the TACC resumes to the last set speed could be activated with the park button.

Thank You


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## BluestarE3 (Oct 12, 2017)

BW984 said:


> The problem appears to be the system combining speed limit warnings with TACC even though they should have nothing in common whatsoever. I found a long thread on this exact topic over on another model 3 forum. Similar Thread Other Forum. I submitted the following to Tesla tonight to officially voice my concerns over this safety issue.
> 
> Hello,
> The current behavior of Traffic Aware Cruise Control (TACC) automatically setting the cruise speed to the GPS database speed limit, even if the car is traveling well below that speed, is dangerous as it results in unintended and rapid acceleration of the vehicle.
> ...


Thanks. I just found that thread too over on the TMC forums. As I noted above, I think it does the same/similar thing even without TACC. So, rather than resuming the previous CC speed as I had assumed, maybe it's also using the map database speed with basic CC? Unfortunately, at the moment, I can't retest basic CC for this behavior since my car is on its EAP trial and using TACC instead of CC.


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## BW984 (Nov 30, 2018)

Until the TACC system is de-linked from the Speed Limit Warning system the best way to avoid unintential acceleration with TACC is to set the Speed Limit to Relative and Offset to -20mph. This way if the GPS speed limit is 65mph and you are traveling any speed greater than 44mph the TACC will not cause you to accelerate and will set at your current speed. This makes the Speed Limit Warning system completely useless as a “you are speeding too fast” warning system but until both systems can work independently I’ll pick more control over the TACC every time.

Ideally in the future you’ll be able to independently set the TACC to whatever speed you are currently driving and if you want to engage the Speed Limit Warning Offset speed you can do that by tapping the speed limit sign on the display. This setup would allow you to set a realistic and useful Speed Limit Warning Offset and allow you to cruise well below that speed if the situation calls for it.


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## BW984 (Nov 30, 2018)

Here is the response from Tesla on my submission:

_Traffic-Aware Cruise Control is a beta feature-always drive attentively and be prepared to take immediate action.

The Autopilot suite of features will continue to expand and improve via over the air firmware updates.

Please direct any questions to technical support at *[email protected]* or (877)798-3752. _

After driving a few days with the Offset at -20mph I have had zero instances of unintended acceleration so I'm happy! It will be interesting to see how this is handled on future firmware updates.


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