Traffic aware cruise control - unsafe?

Traffic aware cruise control - unsafe?

Last week I took my 1 month old Model 3 on a long motorway journey (I live in the UK) for the first time. The road was quiet and I followed my usual procedure on such journeys of engaging cruise control at the speed limit. Being my first time with a traffic aware system it took a short while to get used to pulling out in plenty of time so that the car didn't sense the vehicle in front and ease-off, but I found I could live with that.

What was a complete and very dangerous surprise however was when overtaking a truck, without changing lanes, the car got half way alongside the truck and then braked hard to try and drop to a slower speed than the truck - presumably either anti-collision or trying to achieve the traffic aware minimum of three car lengths?

Whatever the reason, on a windy and wet motorway at night it pitched the car violently sideways alongside the truck. I had to straighten the steering and floor the throttle to prevent either driving into the truck or being hit from behind by other traffic.

If this had been on a busier road or at rush-hour then without doubt somewhere behind me an accident would have occurred.

This wasn't a single isolated incident however. I assumed I had done something wrong or it was a freak circumstance, but happened a further 6 times, each time when passing a large truck where the speed difference was quite significant (anywhere between 20 and 40mph difference) Needless to say I stopped using the traffic aware cruise control on that journey and haven't used it since, because I simply don't trust it.

Perhaps if I understood what was happening and why, I might be able to make allowances and drive around it, but it was so random I don't think it is worth the risk.

If anyone has any explanations or had similar experiences I would love to hear them.

Personally I think this feature on the car is unsafe and certainly not fit for purpose.

Magic 8 Ball | February 13, 2020

This type of "phantom" braking has been reported in the past. File a bug report at ever occurance.

Search the site for "phantom braking".

Magic 8 Ball | February 13, 2020

BTW, although many have claimed: 'it could have caused a wreck' I have not read any reports of people verifying a wreck was caused by this "issue".

Frank99 | February 13, 2020

"pitched the car violently sideways" is not a report that I've heard in the past. Traction control and ABS shouldn't allow anything like this, especially for an automatically generated braking event.

Frankly, I'd make an appointment with the Service Center, and explain to them exactly what you wrote above. What you're experiencing is neither right, nor normal, for a Tesla.

M8B is correct that TACC will occasionally have phantom braking events - you'll be driving down the motorway with no traffic around, and the car will suddenly brake - I haven't experienced anything like a full panic stop level of braking, but I have experienced braking that falls into the "Need to get the car slowed down more quickly than normal" level. Pushing on the accelerator overrides it, but it has pissed off following cars when it does that. It's gotten a lot better, but still isn't gone.

Joshan | February 13, 2020

While not perfect, unsafe is quite a reach. Why do people always have to go to the sensationalist headlines?

Protip: it will never be perfect, what in your life is?

lbowroom | February 13, 2020

" pitched the car violently sideways"

but you were able to recover before it traversed far enough to hit the truck? You have excellent reflexes.

Joshan | February 13, 2020

he also "floored the throttle" to recover from the car going sideways. First time I ever heard of that approach.

Bighorn | February 13, 2020

Programming limits closing speeds now, so it won't speed unsafely by other traffic.

RedPillSucks | February 13, 2020


andy | February 13, 2020

Also in the UK... I’ve not had this with an overtake, but I have had the car recently trying to undertake at speed. The release notes show that there was a code change to deal with speed differences near merging traffic, but the diagram in the release notes is for a Left Hand drive car.

The behaviour you describe would fit with a car trying not to undertake, but with coding for a left hand drive car that’s being driven right hand drive so, rather than slowing to prevent an undertake, it’s actually restricting an overtake.

If it’s any reassurance then I’ve done over 13k miles in my Model 3 on UK roads. It’s mostly driven on motorways and dual carriageways and spends a lot of time on autopilot. Follow the advice in the manual and it works really well.

Things to avoid are using autosteer through roadworks where there is smooth tarmac over old cats eyes holes (it can create an optical lane effect for the car), also lanes where there’s a parallel crack and be careful when going over a the arrow with a side arrow pointing to an exit - the car can see the fork as a lane edge and try and follow the exit rather than staying in lane. Most of the time it gets it right, but you don’t want to be surprised into overriding.

Autopilot isn’t full self driving. It’s a fantastic driver aid giving you more bandwidth to monitor the car and traffic, but you always have to be alert. It’s not designed to be driven without paying attention (illegal to do that anyway) and the car warns you very quickly if it doesn’t feel the right pressure on the wheel to confirm.

andy | February 13, 2020

@lbowroom the side movement happens when the car is tricked by the road surface - arrows, cracks and previous cats eyes from roadworks can cause this.

We’ve had low bright sun at times, so the smooth tarmac over old cats eyes can look like road lines with the reflection of the sun. Similar with a wet surface - and we’ve had bad storms too. You get used to reading the road and making decisions accordingly.

kevin_rf | February 13, 2020

Question, do UK trucks have underride protection? Or is the spaceeideopen and it would be possible merge under the truck (minus the fact you would be decapitated).

Big_Ed | February 13, 2020

TACC would not cause sideways movement. That would be LDA.

vmulla | February 13, 2020

The cars don’t merge under trucks on AP. I tested that after a scare early in my ownership (Feb/March 2018). They would weave in almost trying to merge but would correct themselves, that was the worst of it. By April 2018 that was corrected and the car reliably keeps it's lane even if you try to merge under a truck - even if there is no underride protection.
This observation listed in the Autopilot improvement logs I kept from Jan 2018-July 2018. Unfortunately, some of those observations were flagged by some - they didn't like the idea of bugs being discussed on the forum.

Haggy | February 13, 2020

"Question, do UK trucks have underride protection? Or is the spaceeideopen and it would be possible merge under the truck (minus the fact you would be decapitated)."

Where outside of the US isn't there underride protection? I've seen it in rich countries. I've seen it in Vietnam. It's only the US where people insist that the industry can't afford it.

jnordland | February 13, 2020

It sounds to me like the car slowed due to the difference in speeds between the two lanes. This happens to me on every drive where I'm exceeding the speed of the next lane by 10+ mph (roughly). If you're going 20-40mph faster while on TACC or AP it would certainly slow to a more reasonable passing speed. This was documented in release notes several months back and is visualized on the screen by grey bars in the next lane over showing the speed difference.

FISHEV | February 13, 2020

It was not “phantom braking” but the AP/FSD system working “within normal limits”. It started to pass and got confused and tried to brake out of it. The reason for the braking was the car losing its bearings.

Phantom braking, which is back stronger than ever with 2020.4.1, would be seeing overpasses as obstacles and braking hard at 70 mph on freeway.

The poor adaptive cruise is why I’m selling and going for one of the 2020 EV’s coming later this year. No reason to put up with 2nd rate safety systems. Tesla told me my non working Lane Keeping was also within normal limits.

sheldon.mike1010 | February 13, 2020

God In Heaven! Does your selling mean that you will stop haunting this board?
Am so sick of your 'carping'

PteRoy | February 13, 2020

Phantom braking seems to be completely gone for me with a minor exception. If a car is turning into your lane into a driveway or something and the car is clearly no longer in your way the car will still brake hard as if it’s going to hit it.

On the other hand, there is a stretch of highway not far from where I live where it gets the speed limit wrong and slams on the brakes. The highway is 110@km/hr and it then thinks the speed limit is 80kms then back up to normal then back down again. Annoying to say the least. But meh.

PteRoy | February 13, 2020

Still a better system than my old Acura MDX though.

WW_spb | February 13, 2020

Thanks God Fish is leaving us soon with our super unsafe Tesla's. I don't know what are we going to do without your helpful insight. Good radiance!

Bighorn | February 13, 2020

Tesla is a thinking person’s car. Not all are equipped.

Sarah R | February 14, 2020

@Bighorn Is suggest that a Tesla owner is a thinking car's person.

FISHEV | February 14, 2020

"Phantom braking seems to be completely gone for me with a minor exception."

Except you have "remembered" two major exceptions, actually the one is not a a case of phantom braking, the other is. Always interesting that the phantom braking is one of the more commonly and constantly eported issues with Tesla's adaptive cruise but to fanbois it's a feature.

sheldon.mike1010 | February 14, 2020

Fish's mom dropped him on his head more than once.

lbowroom | February 14, 2020

Confusion and losing ones bearings are human traits, not computer traits.

we know you're not selling anything....

teslamazing | February 14, 2020

Magic 8 Ball | February 13, 2020
BTW, although many have claimed: 'it could have caused a wreck' I have not read any reports of people verifying a wreck was caused by this "issue".


Lots of "glad there wasn't anyone behind me" Are you really glad? I think the car knows and would take the immediate correct action to prevent an accident.

crmedved | February 14, 2020

A video would be nice.

ellett | February 16, 2020

Whether it's phantom braking or confusion about which lane a nearby car is in, Teslas do "flinch". It's something you have to be aware of and hope will get better.

Geico | February 16, 2020

FISH is pointing out a valid point though. As unfortunate as it may seem, software updates usually do end up breaking something while fixing another.

I've ridden in some Ford's with the Copilot 360 system and it works surprisingly well (the Mach E is getting a better version of this). Really the only difference is it doesn't take off ramps and doesn't change lanes. The Tesla autopilot does a bad job at both, I initiate the manual lane changes and don't take off ramps. But the Nural Net will make it better they say!

Just like how well the automatic windshield wipers work using the nural net xD. Still broken and leaves me putting them in manual in mist and light rain. Good times owning a Tesla. Maybe in 15 years when they get enough data they'll have the windshield wipers figured out.

Geico | February 16, 2020

For some reason the legacy automakers rain sensors work great, but Tesla thought the nural net had to be used on the windshield wipers. LOL

andy.connor.e | February 16, 2020

you should take a trip to six FLAGS

WW_spb | February 16, 2020

Lol Trolls are no fire before tonight

WW_spb | February 16, 2020


WW_spb | February 16, 2020

Trolls are on fire tonight lol

WW_spb | February 16, 2020

And I am way to sleepy for this bs

GHD SPORTS APK | February 17, 2020

Traffic-Aware Cruise Control: This is called “adaptive cruise control” in other cars. It lets you set a top speed and keeps you a certain distance from cars in front of you, even if they slow down. ... You can activate it when the car senses you are in a lane, and its job is to keep you in that lane.

keith | February 17, 2020

@PteRoy: Agree with your comment. If anything TACC tries to be too safe. It will brake when it sees a car turning across one's path, even if the crossing car is going to be well clear by the time you reach it. When assessing other vehicles TACC is really good at sensing their component of velocity in the same direction as your own, but quite poor at assessing the velocity perpendicular to your own (across your path). The other thing that throws it is a paper bag or tumbleweed or similar blowing across the road. A human driver does not slow down for these, but TACC sure does! (in my experience).

keith | February 17, 2020

@OnmoviesApp: "You can activate it when the car senses you are in a lane, and its job is to keep you in that lane." I think not! Unless I am mistaken TACC controls your speed but has no part in deciding your direction; that is up to you unless you engage AP.

nigel | February 18, 2020

From the sounds of responses so far - I think I will stick to enjoying driving my Model 3 using my own brain, hands and feet - that way I know I will have fun and I can get myself out of whatever I got myself into. And on days when I want a bit more excitement I can always hit the gamble button and use TACC
Suspect the savage braking was the car preventing an undertaking manoeuvre - not realising it was in the UK where we still drive on the left.

ReD eXiLe ms us | February 18, 2020

"What's behind you, doesn't matter." -- Enzo Ferrari

My younger Brother hates the way I drive in traffic. He says I drive 'too close' to other cars. Keep in mind, I do no such thing. I purposely make sure to leave a two car length minimum between myself and other vehicles at any speed. However, at traffic lights, I may reduce that to about one car length.

Years ago, he had been drinking at a party at his house. He went somewhere, without telling ME of course, and ended up getting his Suburban totaled on the freeway when someone ran into the back of his truck. Apparently, they pushed him forward into another car stopped in traffic. He stopped drinking entirely after that, but never blames the alcohol or the long line of stopped vehicles that were ignored by a speeder in the night.

lbowroom | February 18, 2020

How many more fish reinforcements should we expect?

Joshan | February 18, 2020

how many fake email accounts can he open?

ameetm3 | February 19, 2020

I got rear ended due to the TACC. The car braked VERY hard due to traffic ahead and the car behind me was not able to stop in time. If I wasn't using TACC / Autopilot, I would not have braked so hard and the accident would not have happened. 100%. And then there is Phantom braking. I have had it a few times but Tesla says it is normal behavior.

Since that incident, I don't use TACC at high speeds. The non Teslas around us are still not ready for Automatic driving. Similar incident happened to a friend of mine. Her car got rear ended to to sudden braking.

However, I still find TACC very useful at low speeds / traffic.

ReD eXiLe ms us | February 19, 2020

Wait... What.. What's that smell? (What's that smell?)
What's that smell? (What's that smell?)
Lots of stanky [BOLSHEVIK]!

WW_spb | February 19, 2020

Nuke thread please