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Car adjusting speed for Speed Limits ?

VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,757
6,326
Surrey, UK
Moderator comment - latter part of thread merged from "Confused about cruise control" which may contain references to more recent functionality

There is some confusion about whether, when on TACC (traffic aware cruise control or Autopilot) the car changes speed for speed limits - whether GPS/Maps or the new visual speed sign detection.

Officially, "When cruising at the speed limit, the cruising speed does not change when the speed limit changes". But it will adjust its speed "When cruising behind a detected vehicle," and "when entering and exiting [some] curves" (my italics).

upload_2020-9-11_8-0-3.png upload_2020-9-11_8-1-59.png

However some suggest that their vehicle adjusts its speed based wholly on GPS/Map based or the new (2020.36.x) visual speed sign recognition.

How does your vehicle behave? Have you found any settings that control this? Is it totally reliable/consistent? Has it ever slowed in time for the change in speed limit to remain legal?


Apologies for the disjointed poll options. I accidentally posted the poll prematurely, it did not allow me to delete and my edit options were limited.


Moderator comment - historical poll subsequently deleted as options no longer reflect more recent observations. Original poll results below.

1617649916054.png
 
Last edited:

NorfolkMustard

Active Member
Apr 18, 2019
2,216
2,204
M3P w/FSD
Definitely. Only occasionally, but consistently at certain places. Buy me a gopro and mount and I'll show it :)

Anecdotally, it's been where there are speed cameras nearby too. Perhaps it only does it where it has a very high confidence :- map + fleetspeed ? and with it now reading signs it will start to do it more as it'll have more first-hand corroboration
 
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Pink Duck

Member
Jan 28, 2020
116
59
South Norfolk, UK
I find if TACC is set to the determined speed limit and remains on then AP will raise target speed up and down as further determined limits happen. Except I typically stop TACC ahead of a lower speed limit at the point that the car should be slowing to allow regen to meet the new limit, but then re-enabling TACC after that alone stops the limit matching. A pull and hold of stalk to set target speed when already active at the same seems to be necessary to restart the auto-speed changes thereafter.
 
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VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,757
6,326
Surrey, UK
Definitely. Only occasionally, but consistently at certain places. Buy me a gopro and mount and I'll show it :)

Perhaps it only does it where it has a very high confidence :- map + fleetspeed ? and with it now reading signs it will start to do it more as it'll have more first-hand corroboration

Fleetspeed could probably cause those slow downs. Much like it does already for some corners, intersections or at final stages of an exit slip.

Now that we have visual, you could go out and see if putting a bin liner over the sign makes any difference :D. I would be happy to buy you one of those :p
 
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VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,757
6,326
Surrey, UK
I find if TACC is set to the determined speed limit and remains on then AP will raise target speed up and down as further determined limits happen. Except I typically stop TACC ahead of a lower speed limit at the point that the car should be slowing to allow regen to meet the new limit, but then re-enabling TACC after that alone stops the limit matching. A pull and hold of stalk to set target speed when already active at the same seems to be necessary to restart the auto-speed changes thereafter.

Sounds like you have an S or X. What version autopilot? Same question for @henleyregatta and @Alex987854 or anyone else that said that their car slows down and speeds up
 

henleyregatta

Member
Dec 17, 2018
108
82
Hampshire
Sounds like you have an S or X. What version autopilot? Same question for @henleyregatta and @Alex987854 or anyone else that said that their car slows down and speeds up

I have an S, 2018 with AP2.5.

If under "full" autopilot - not just TACC but AutoSteer - then if I have set speed to (say) National Speed Limit and I pass through a village/area with a speed restriction (50/40/30), then the car will first slow down to that limit - all be it after passing the sign, not before - and when the limit goes back up then speed will go back up to the limit I'd previously set.

If I've set a lower limit - engaging AutoPilot within a 50/40/30 area at the defaults - then the speed will not go up when I pass a national speed limit sign; it never exceeds the speed first set on engagement.

This does not apply on all roads, I've had more success on smaller roads than bigger (around here, works great on the A272, less well on the A3 at the 50 limit at Guildford). I expect this is because it's using incomplete GPS / Map data rather than sign reading (and if there's no data in the database for the road, there's no changes).

Car also slows to take corners, particularly on slip roads and smaller roads.
 

Tonybvi

Member
Jul 28, 2019
371
326
NE Scotland
Changing my vote after a drive today. 60 -> 30 -> 60 all done automatically for me just now.

Not had a chance to try in anger yet with the latest update but out of interest was this just with TACC set (and if so was it set at your driving speed or the speed limit?) or did you need to engage FSD as well before it would do this?
 

roadcred

Member
Aug 23, 2019
198
118
UK
More concerned that it no longer picks up changes in speed limits by the Council. All these 20 mph limits round us are not recognised. What is worse is that my Volvo collects these modifications and is bang up to date and Waze also is up to date!
 

pgkevet

Active Member
Jul 1, 2019
1,508
1,345
mid wales
More concerned that it no longer picks up changes in speed limits by the Council. All these 20 mph limits round us are not recognised. What is worse is that my Volvo collects these modifications and is bang up to date and Waze also is up to date!

Are those red or black bordered speed signs? As I understand it the black ones are advisory and the reds are legal limits.

pgk
 

Joelly

Member
Oct 29, 2019
473
203
United Kingdom
Using TACC, the car remains constant
Using auto steer the car changes to what it believes the speed limit is.
I have experienced both slowing slightly for a bend at various times.
 

Avendit

Member
Apr 18, 2019
857
567
EDI
During lockdown I had cause to do Edinburgh - Inverness a good few times. This a mix of fast a road and dual carriageway, swapping back and fore.The roads were empty so I could experiment with autopilot.

Mixture of versions tbh, but all behaved much the same.

Coming onto a dual carriageway, it would pick up the speed limit change fairly accurately based off map data, then 1/4 mile later, apply it. Coming out of the dual areas, much the same, but it seemed to apply the lower limit, as someone else said, just in time for the first of the average speed cameras. Which is also about 1/4 mile later, on average.

I think it's just lazy. If I was in traffic that would have felt like a very long 1/4 mile each time.

It did pretty well otherwise, with supervision, but that's another thread.
 

GRiLLA

Member
Jul 5, 2020
977
985
UK
So my theory is this, in a Model 3 LR.

If I set AutoPilot in a 50 it will drop to 30 after passing a sign, message on the screen that Autosteer has reduced the speed. When the speed then does back to 50 it will speed up again.

It won't accelerate past the speed limit when you first set it, and if anything else disrupts it during the 30 (like taking back steering but leaving TACC) it'll then stay at 30.
 
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Tonybvi

Member
Jul 28, 2019
371
326
NE Scotland
Using TACC, the car remains constant
Using auto steer the car changes to what it believes the speed limit is.
I have experienced both slowing slightly for a bend at various times.

Exactly my experience on my Raven MX. TACC the car just carries on at same speed although it recognises the different speed limits, using FSD (effectively auto steer when navigate on autopilot is not available) the car slows down and speeds up as per the speed limits.
 

Dilly

Active Member
Feb 24, 2020
2,356
1,893
Norfolk
I voted yes - sometimes.
If I put it straight into AP and leave it there, it will change up or down about 100 yards after the sign. The caveat to that is that it doesn’t always know the correct limit from gps, database or whatever.
Conversely, TACC alone doesn’t change.
The stupidity comes where AP was engaged and changing speed but was disengaged and then re-engaged whilst leaving TACC active. In this state, speed limit charges aren’t made by AP even though it is active.
Cancelling both AP and TACC and re-engaging AP will allow speed limit changes.
 
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Tonybvi

Member
Jul 28, 2019
371
326
NE Scotland
The latest software update uses the cameras to identify speed limits. For example in our local town we have a temporary 20mph limit to enable “spaces for people” (Covid 19 pavement extensions). The car identifies these limits via the cameras and applies them if I am on FSD. It also now stops automatically at traffic lights when on FSD.
 

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