Auto Pilot Won’t Undertake?

[AndyEVTM3]

Hi,
I was driving home last night in the dark on an unlit 3 lane A130.
I was in lane 1, which was clear ahead for a long way and I had the auto pilot cruise control set to 70.
My car (model 3 2022) was happily driving at 70 when it started to approach a car in lane 2 doing about 65.
My car then slowed down to the same speed and sat behind the car which was in lane 2. I remained in lane 1.
The other car was clearly in lane 2 as it was shown on the display in my car and there were no other cars around. I.e just me in lane 1 and the other car in lane 2.

Question is was my car refusing to undertake or is there another reason it slowed down?

Thanks for any advice or info.

 

[Burley]

Just a brief, gentle press on the throttle would have got your car to have passed the car and AP would have then regained your set speed, such as if you'd now moved into a exit lane for another road, so weren't technically undertaking. So you can over-ride the refusal to pass on the left with a brief tap on the throttle - obv only where legal...

 

[Pandinium]

I honestly find the AP more hard work than just driving - it’s too whiney at the moment, indicate then slightly steer (which uses more effort than just steering the car?!) then panics and aborts still… the adaptive cruise control is about as far as I trust it.

I am curious about the “undertaking” I was under the impression if lane one is moving faster than lane two without breaking the speed limit or intent to undertake than it was ok to pass them, ie middle lane nob head sitting at 60 when the outside one is empty, and your just staying in that lane not going back to lane 2…

 

[Medved_77]

I am curious about the “undertaking” I was under the impression if lane one is moving faster than lane two without breaking the speed limit or intent to undertake than it was ok to pass them, ie middle lane nob head sitting at 60 when the outside one is empty, and your just staying in that lane not going back to lane 2…

There are some exceptions to when undertaking is allowed, generally fine at slow speeds when in congestion.

I watched this a while ago if you want a detailed answer:

 

[Fursty Ferret]

I trundle past people in the inside lane all the time. Provided you have somewhere to go* (hard shoulder etc) it's much safer than making the point of swerving across three or four lanes and back again. It's not like the person in lane 2 is going to realise that they shouldn't be there.

For what it's worth, it needs only a small prod on the accelerator. If you watch the visualisation you'll see the "lead" car turn from black to light grey, which means it's no longer controlling your speed. Once you've done this it'll ignore traffic on your right until you change lane unless it's stationary, when it'll slow down anyway.

* risk is subjective. At 2am you'll find me in lane 2 of any empty smart motorway section without a hard shoulder, as I've come across stranded vehicles with no lights or reflectors in lane 1 before now. I'll move over and back again if someone comes up behind me.

 

[AndyEVTM3]

But not curious enough to look in the manual

Don’t have to look in the manual because there’s always people on these forums I can ask (like you I presume) who know more about these things than the Tesla software Engineers do!

 

[debrooker]

Question is was my car refusing to undertake or is there another reason it slowed down?

Thanks for any advice or info.

If you dab the accelerator it will proceed to undertake

 

[interbear]

I’ve had my Model Y slow down when on autopilot several times to avoid “undertaking” on a motorway when someone is hogging the middle lane and going slower. So I do think it’s deliberate / part of the feature to comply with the law on this.

Same happened when driving our VW campervan to Scotland and back last weekend, so I think it’s standard practice with any vehicle with “traffic aware cruise control” (TACC).

I would add that the TACC experience on the VW van is significantly better, more relaxing than the Tesla implementation in my opinion. It doesn’t brake when going past exits and it automatically accelerates a bit when indicating to overtake, whereas in my experience the Tesla moves to the outside lane, thinks about it for a bit and then accelerates to overtake. The VW is smoother all round in fact. The only improvement I’ve seen with Tesla TACC is than phantom braking is now a much rarer occurrence than it was.

 

[Mrklaw]

does it deliberately. If you give the accelerator a nudge it’ll give the car ‘permission’ and I think after that it’ll pass other cars too (but not absolutely certain of that part)

 

[Louis0w]

This behaviour is deliberate and explained in the TACC portion of the Manual :

 

[MrBadger]

For those unaware, the last part of that is quite important to know imho - its ability to try and speedily undertake other vehicles has tried to catch me out a few times but now I am aware of the scenario, its easier to know what is going on and what signs to look out for. There is also another behaviour that is similar, but not the same circumstances.

tl;dr
1: Don't assume a lane change will revert the functionality not to undertake
2: The car will be following/speed tracking the dark/light (day/night mode dependent) vehicle which is not necessarily the vehicle that you are about to undertake

These are over and above the 50mph cutoff.

I have FSD/NoA and would not like to 100% agree with the 'until you change lanes' part of this as I am pretty sure that I have changed lanes under auto lane change and still had the car try an undertake even though no use of accelerator. I suspect though that its definition of 'change lanes' is a little different to mine and may have changed recently when they changes off ramp behaviour so this behaviour may now be outdated. The scenario that I had was joining a motorway (for those that know, M25 J11? clockwise at Chertsey) then shortly exiting under NoA and joining M3 at J2 to continue 'south'/west. This involves a, exit lane, then a lane split for which the car use to indicate, then short intersection before joining the M3, usually on a dedicated lane, but sometimes on a merge (depending on what lane NoA decided to take at the former lane split). This was not enough to be classed as 'change lanes' to cancel the undertake feature - its common to be in slow traffic and override speed heading briefly on M25 up to the interchange which I think is what was triggering the undertake override as ~5 - 10 minutes up the M3, the car would still be ignoring the undertake block and try and undertake even though no speed override had taken place since being on the M25.

The other scenario where the car may try and undertake is if a car pulls adjacent to you and does not pull sufficiently far ahead for autopilot to treat it as the follow/tracking car. So if it then slows, autopilot will merrily ignore it and you will undertake. The follow car is the car highlighted on the screen visualisation in dark/lighter shade (depending on day/night mode) and it is that car which will be governing your speed, not necessarily the one that's just pulled ahead of you. It can take quite a significant distance ahead before autopilot switches the follow/tracking car to the one that just passed you.