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Forward collision warning

We've owned our Model 3 for two weeks. Today, out for a ride, the Forward Collision Warning and Automatic Emergency Braking did something that seemed wrong.

Driving north on a two lane road. Up ahead a big SUV pulls out from the right side, crosses in front of me, and heads south. There was plenty of room. I had the cruise control on but if not I wouldn't have let up on the accelerator at all. My car braked pretty hard. It all happened so fast I didn't have time to look at the touchscreen and I didn't notice a warning chime. My wife was in the passenger seat and did hear the warning chime.

I quickly looked in the rear view mirror, afraid we were going to be rear-ended. Luckily, no one was behind us.

Home now, I check the owner's manual and learn that Automatic Emergency Braking will release the brakes when the car has slowed down by 30 MPH. Or by turning the steering wheel, press/release the brake pedal, accelerate hard or the object is no longer detected.

I saw that Forward Collision Warning is adjustable. Late, Medium and Early. Maybe the "Late" setting would be better? Any advice?
 
We have had it happen a couple times now in 5 weeks of driving our M3.
After a couple of these events, I have gone back and watched the dashcam video and they were all closer than I thought at the time it happened.
We decided we would have let off the gas in an ICE car and been ready to apply the brakes, it's a tough call, it is almost as if there's extra caution built in just in case the vehicle pulling out has a problem.
 
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Knightshade

Well-Known Member
Jul 31, 2017
15,424
28,774
NC
We've owned our Model 3 for two weeks. Today, out for a ride, the Forward Collision Warning and Automatic Emergency Braking did something that seemed wrong.

Driving north on a two lane road. Up ahead a big SUV pulls out from the right side, crosses in front of me, and heads south. There was plenty of room. I had the cruise control on but if not I wouldn't have let up on the accelerator at all. My car braked pretty hard. It all happened so fast I didn't have time to look at the touchscreen and I didn't notice a warning chime. My wife was in the passenger seat and did hear the warning chime.

I quickly looked in the rear view mirror, afraid we were going to be rear-ended. Luckily, no one was behind us.

Home now, I check the owner's manual and learn that Automatic Emergency Braking will release the brakes when the car has slowed down by 30 MPH. Or by turning the steering wheel, press/release the brake pedal, accelerate hard or the object is no longer detected.

I saw that Forward Collision Warning is adjustable. Late, Medium and Early. Maybe the "Late" setting would be better? Any advice?


Realistically, Teslas basic AP features (TACC and Autosteer) are meant for highways where cross-traffic does not exist.

They operate on the assumption all traffic is going the same direction as you-- so if it sees a vehicle sideways ahead in your lane, it assumes someone is blocking your lane, not in the middle of crossing it in a 90 degree turn, and brakes.


Page 83 owners manual said:
WARNING: Do not use Traffic-Aware Cruise control on city streets or on roads where traffic conditions are constantly changing

Autosteer is even more explicit about this:


Page 89 said:
Autosteer is intended for use only by a fully attentive driver on freeways and highways where access is limited by entry and exit ramps



The good news, assuming you have FSD, is the beta software that's allegedly going to be available very shortly will do 2 things:

Enable city streets code that understands things like cross traffic properly

and

Removes use of radar as a sensor input, which often causes unneeded braking events
 
Realistically, Teslas basic AP features (TACC and Autosteer) are meant for highways where cross-traffic does not exist.

They operate on the assumption all traffic is going the same direction as you-- so if it sees a vehicle sideways ahead in your lane, it assumes someone is blocking your lane, not in the middle of crossing it in a 90 degree turn, and brakes.

Page 83 owners manual said:
WARNING: Do not use Traffic-Aware Cruise control on city streets or on roads where traffic conditions are constantly changing
Page 89 said:
Autosteer is intended for use only by a fully attentive driver on freeways and highways where access is limited by entry and exit ramps

I see. I've been through the user manual twice, but I guess I need to read through it again. Maybe a little slower and more thoroughly this time.

Fancy new car with great technology. It was too much to resist, I guess. Thinking back on yesterday's incident, had I been in my old ICE car, it never would have crossed my mind to use the cruise control on a road like that.

On a previous day, we had an experience on another two lane road where the Tesla started braking for a green traffic light. I knew to hit the accelerator and we continued through the intersection. But that was a little unsettling too. I've always thought one of the main causes of accidents is cars stopping in places that other drivers wouldn't expect there to be a stopped car. So I definitely don't want my Tesla stopping in a place where other drivers won't be expecting it and maybe not paying 100% attention.

But that makes perfect sense. TACC and AP for highway use only.

Many thanks for your post!
 
The aspect of collision warning and braking seems logical enough and have even experienced where a vehicle has driven on the line and triggered it. Seems like it is doing what it should.

However, have experienced a couple of odd situations where I am curious if anyone has any insight...

First, motorcycles coming from opposite directions ALWAYS trigger the alert and braking. Have been paying attention to where the motorcycle is in the lane to see if they are touching the line or not, and they are not. Seems if the motorcycle is anywhere past the midpoint of their lane to the center of the road (and not on or near the line), it triggers. It has gotten to the point where if I see a motorcycle I anticipate the issue and turn off auto until they pass. Any insight about this is welcome.

Next, driving with no cars around at all, suddenly the collision warning goes off but no breaking. Almost seems a moment that a bird flew by or something, but cannot put my finger on it. I thought maybe sensors were dirty or something and gave everything a wipe down...still happens.

Are these things I should call Tesla out for an adjustment, is it normal, or ??
 
motorcycles
While on autopilot in California traffic, a motorcycle was lane splitting and my car did the brake thing.
The car suddenly thought I was closer to the biker than the 3 car length following distance I had set and it dramatically slowed down.

I felt the need to slap the smile pedal because that could have caused a rear-end accident. (looked like I brake checked someone)

driving with no cars around at all, suddenly the collision warning goes off but no breaking
Might be a symptom of 'phantom braking'
Don't listen to people when they tell you 'its fixed' cuz its not.

My car slammed on the brakes while going under a bridge but no warning chime (no traffic in front of me)
Again I smashed my smile pedal in fear someone would rear-end me.

Got the car at the end of June of this year, so its still brand new.
no FSD
 
I want to formally validate the AEB concern people are having.

I was following along in traffic yesterday.
I approached the car in front of me as it started to pull away.
I did get close, maybe less than 5 feet.
My AEB activated and smashed the brakes.
My foot was already on the brakes during the approach and I felt it dig itself into the floor board.
My approach was slow, brake usage was minimal.
I couldn't even get it going again by hitting the gas or brake so my car stopped itself for about 3 seconds on the highway.

I've been driving the same way since I got the car in June and I now agree that the latest patch did something to the AEB activation sensitivity.
I've turned AEB off for now.

I don't think these safety systems are designed for alert/attentive drivers.
I'm sure many improvements are on their way, AI day looked great.
 
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This car isn't safe, it is stupid...I've turned all this crap off. Lane avoidance, brake/emergency assist...I must have accidentally turned it on the emergency braking, and a car did the same thing this morning in front of my daughter and I. The car goes full on anti lock brake when there is zero chance/danger of us ever getting close as a car who sees us coming, pulls out in our lane, yet keeps going across two lanes to the far left....she almost dropped her coffee in her hand.

Turned that off...again ASAP. All "safety features" are off on my car. They are useless and dangerous. Only to driver's without a clue and might not be very good driver's it would be helpful at times...but to most people....nope. That is why Tesla's AI and Elon's BS is complete nonsense....we won't have self-driving cars in my lifetime. Classic example TS posted of stuff a car can't figure out and assume and watch behavior of somebody. It just knows, hey...car, slam on brakes...not...hey car...oohhh...they are going to continue across these lanes and I won't hit them, like people think.

Also, does stupid things on a slight curving road...cars next to you slightly ahead...car will lift off accelerator, or cars coming opposite way...car will slow like we are about to go head on into someone. And funny thing, the blue lines shows a curved road...it obviously doesn't have any AI...just bad programming by a coder.
 

john5520

Active Member
Mar 3, 2020
1,203
1,111
Florida
As much as I think I'm a great driver, the FCW has saved me a couple times when, in the split second my attention was somewhere else, I heard the warning and recovered. Whether I would have reacted in time without it, I don't know. I haven't had a fender bender in about 12 years, but it was still nice to have that warning. I have mine set to medium.

As for the car using AEB (with AP off), never had it happen. Even when the FCW warning sounded, I never had the car brake on its own. I guess I was never close enough for it to activate.

One the other hand, with AP on, I've experienced the braking for turning cars like the OP described. The system can overreact for crossing traffic. It's something you'll have to pay attention to if using it off highway. From my usage, it seems to have gotten better over time (with OTA updates), but depending on your speed (and that of the crossing vehicle), it can brake harder than expected at times.
 

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