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Is this normal behavior for AP?

Whilst leaving the A1(M) the other day I was using AP and on the way up the slip road it started slowing down - the car in front was so far away that I knew it couldn’t be that making AP slow down so I glanced at the screen to see that the “MAX” number (ie the speed I had set for AP) was also reducing.
I’m used to AP slowing down and speeding up as per the surrounding traffic conditions but I’ve never seen the set speed changing automatically like that.
I tested it again on the way home (different slip road) and it did it again.
 

Dilly

Active Member
Feb 24, 2020
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2,755
Norfolk
Whilst leaving the A1(M) the other day I was using AP and on the way up the slip road it started slowing down - the car in front was so far away that I knew it couldn’t be that making AP slow down so I glanced at the screen to see that the “MAX” number (ie the speed I had set for AP) was also reducing.
I’m used to AP slowing down and speeding up as per the surrounding traffic conditions but I’ve never seen the set speed changing automatically like that.
I tested it again on the way home (different slip road) and it did it again.
I’ve not seen this but way back it was slowing for bends for a while. I’ll key an eye out. I’ll be using slip roads today
 
I've just read the manual that you posted. It appears that they explain clearly the limitations of the TACC. and warnings of what may happen.
Warning
Traffic-Aware Cruise Control may occasionally cause Model Y to brake when not required or when you are not expecting it. This can be caused by closely following a vehicle ahead, detecting vehicles or objects in adjacent lanes (especially on curves), etc.

Warning
Due to limitations inherent in the onboard GPS (Global Positioning System), you may experience situations in which Model Y slows down, especially near exits or off-ramps where a curve is detected and/or you are navigating to a destination and not following the route.
 

Mrklaw

Active Member
Mar 5, 2020
1,779
1,146
Berkshire
I can't imagine using it on slip roads at all - are we talking on or off slips? TACC is for stable driving, and slip roads are where I'm likely to want/need to adjust speed to the traffic on the main road so I'd want full control. And certainly not AP I can't imagine it much likes diverging/converging lines and I don't want any unwanted movement when I'm blending with traffic.

EAP with nav on autopilot and 'it takes off ramps' also confuses me - I saw a couple of videos and it just seems to (late) leave the main road and then immediately disengage leaving you to take over? Nav will indicate the exit anyway, so just leave yourself - whats the difference in a couple of seconds between it dropping out with no warning, vs you turning it off when you are ready for it?
 
I can't imagine using it on slip roads at all - are we talking on or off slips? TACC is for stable driving, and slip roads are where I'm likely to want/need to adjust speed to the traffic on the main road so I'd want full control. And certainly not AP I can't imagine it much likes diverging/converging lines and I don't want any unwanted movement when I'm blending with traffic.
Yeah, for me perhaps "slip roads" wasn't accurate. I have in mind where the A48(M) crosses the M4 leaving Cardiff (there is a slip about 1/2 mile ahead) and bizarrely coming in the opposite direction where you just filter from one motorway to another, it brakes after the filter. Also M48 crossing the M5 into Bristol/Avonmouth, there's a long sweeping right which it likes to take at 65. The problem is that the speed transition isn't gentle - it's not a phantom brake, but it's extremely noticeable and its another Tesla foible that spoils the experience for passengers particularly.

On classic sliproads, or offslips at least, the same system works because you can leave at 70 and it'll progressively set the limit down as you approach a roundabout.
 
I’m used to AP slowing down and speeding up as per the surrounding traffic conditions but I’ve never seen the set speed changing automatically like that.

It’s basically known as fleet speed. Tesla gather speeds on sections of roads from its fleet then apply it as a speed limit at motorway interchanges and off ramps (and I suspect other scenarios too).

It’s often very different to speed limits, does it in approx 5mph steps so not particularly smooth (at least pre v11) and at off ramps if you have EAP/FSD NoA, will often coincide with the NoA will exit in xxx ft message.

 
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I see this all the time coming off the A303 on to the A3093. If I have TACC engaged then it will slow to 55 just after I exit, then 45 in the sharpest bend and then speed up again to 55. Then as it approaches the roundabout it slows its self down to 25. I wouldn't mind as the speeds are sensible but it puts the brakes on far too harshly compared to how a human would to make it comfortable.
 
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It’s basically known as fleet speed. Tesla gather speeds on sections of roads from its fleet then apply it as a speed limit at motorway interchanges and off ramps (and I suspect other scenarios too).

It’s often very different to speed limits, does it in approx 5mph steps so not particularly smooth (at least pre v11) and at off ramps if you have EAP/FSD NoA, will often coincide with the NoA will exit in xxx ft message.

This is fascinating… I particularly liked the 2019 posts saying “this is going to get me in an accident” and “I just want basic cruise”
Looks like fleet speed is reading from the wrong motorway in my experience- the one I’m travelling over, under, or alongside
 
This is fascinating… I particularly liked the 2019 posts saying “this is going to get me in an accident” and “I just want basic cruise”
Looks like fleet speed is reading from the wrong motorway in my experience- the one I’m travelling over, under, or alongside

Another potential scenario, which I got reminded about this evening when it occurred again, is that if you have a nav destination set and it wants to take you off at a particular junction, but you decide to not come off there and continue on the motorway, the car will behave as if it had just come off at that junction and reduce your speed as if you were travelling up the offramp - even though you are on the fast lane of the motorway...o_O a quick twiddling of thumbwheels to restore the speed - no need to resort to overriding with the accelerator.

Caveat, I have NoA enabled at start of any drive, but today I was only on TACC. So not sure if this is NoA functionality or general Autopilot functionality.
 
Thanks for all the replies guys, I’m suitably reassured. Both off ramps (perhaps slip road was the wrong expression) were fairly straight and were leading up to roundabouts, both times I was on TACC only. The first time it happened I was in one of those “stay in this lane to exit” lanes hence TACC not disengaging automatically as I didn’t have to indicate, wouldn’t have noticed otherwise, the second time I deliberately re-engaged TACC to confirm the behaviour - when the “MAX” speed dropped to 25 I disengaged TACC as I wasn’t sure whether the car would stop at the roundabout or just blindly go on its way regardless of traffic.
Interestingly I had noticed previously that TACC would slow the car on one bend in particular near here, but the “MAX” speed didn’t change in that case, and I don’t think it slows down for that bend since the v11 update.
 

Mrklaw

Active Member
Mar 5, 2020
1,779
1,146
Berkshire
Another potential scenario, which I got reminded about this evening when it occurred again, is that if you have a nav destination set and it wants to take you off at a particular junction, but you decide to not come off there and continue on the motorway, the car will behave as if it had just come off at that junction and reduce your speed as if you were travelling up the offramp - even though you are on the fast lane of the motorway...o_O a quick twiddling of thumbwheels to restore the speed - no need to resort to overriding with the accelerator.

Caveat, I have NoA enabled at start of any drive, but today I was only on TACC. So not sure if this is NoA functionality or general Autopilot functionality.

I assume thats GPS resolution related - it assumes you’re doing what it told you to do until it can properly tell you aren’t in that lane. See it a lot when it takes a while to reroute because it doesn’t know you ignored the junction yet.
 
I assume thats GPS resolution related - it assumes you’re doing what it told you to do until it can properly tell you aren’t in that lane. See it a lot when it takes a while to reroute because it doesn’t know you ignored the junction yet.

I would like to think that the car knows roughly what lane it is in and at least enough to know whether it is heading up and off ramp or not - it a fundamental requirement of auto lane change and NoA off ramp (although the latter is rather late to respond on many occasions).

I have had it start to think that I am heading up an off ramp (I think it was around Oxford on London bound M40) even though navigation was clearly to continue on M40 towards London, so I am not convinced that navigation (at least in all similar circumstances) is used as a further hint of where it is. But that may have changed, or, in good Tesla fashion, 'it depends' on the probability of each scenario outcome.

I would think that it is an indication of how confident that Tesla have in its geospatial analysis though and what it prioritises (eg gps vs vision vs navigation etc) in what circumstances. Whatever way, it is far from perfect - lots of evidence of car slowing to speeds of parallel adjacent roads, or even more baffling, suddenly assuming that the car is on a road that is either an overpass or an underpass. I turned off FSD's stop sign control due to the car reacting mid motorway or Hindhead A3 tunnel because it though it had just come across a traffic light and wanting me to confirm that it was safe to continue - so it definitely does not realise that, at least on our roads, its pretty unusual to get traffic lights mid motorway or dual carriage ways when no interchange/junction is close by. A case where vision is being prioritised over map data and common sense.

I would like to think that when single stack combines FSD city streets beta advances with our highways code, some of these, and several other issues (such as being able to ignore road signs in adjacent streets) will go away. I have always said, and still believe, that had Tesla put as much effort into highways as they put into city streets, that Level 4 on our motorways and major divided A roads (ie for many, the most beneficial cases) would be achievable relatively quickly. With single stack and Level 3 legislation now/soon allowing, Tesla will be in a position to show their capabilities and, tbh, deliver on FSD for many peoples needs - I for one am not bothered about the car driving me home from the pub, but driving me with hands off to Warrington or wherever for the motorway portions of the journey would be by aim. Tesla just need to show the will.
 

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