AutoPilot encountering stopped traffic

AutoPilot encountering stopped traffic

New owner - took delivery in late March, love the car so far. I ride as often as possible, and drive when I must ;)

One question I have for the forums is around a highway (not freeway) on my commute. The speed limit is 60mph, and there are about a half dozen stoplights, some of which are right after slight bends in the road. On AutoPilot, often times there's nobody in front of me for a good while, but I see stopped cars at the light ahead. So far, AP has not initiated any braking prior to my comfort level, so I've disengaged AP in all of these scenarios. I can easily see the stopped traffic as a human, but I can see where it might be harder for the car to extrapolate the curvature of the road and know those stopped cars are in my lane, but I haven't been brave/foolish enough to really test it, and have bailed out and manually started slowing down. How far down the road, especially a curved road (not a blind curve) does AP look? So far I'm pretty sure that it would have to SLAM on the brakes if I let it come around to find those stopped cars, but I haven't pushed the limits yet. I don't feel like I'm over-cautious, but I'd also like to trust the car to see stopped traffic up ahead even while going over 60mph around a gentle curve and slow down fairly gradually.


jimglas | 17 April 2019

At this time AP is for freeways only

Tronguy | 17 April 2019

So, the deal is that the radar in the car can only pick up closing speeds below a certain number, like 45 mph or something. Otherwise, it'd be freaking out on opposing traffic. That's how people with autopilot get into serious trouble - it won't detect a stopped truck when you're doing 70. This is pretty well spelled out in TV he manual.
You _have_ read the manual on a beta feature on a car that can kill you, right? Or are you living in fairy tale land?

TexasBob | 17 April 2019

Do NOT do this PLEASE.

Kary993 | 17 April 2019

moderated forum are very useful in these cases.......

pyee78 | 17 April 2019

Tronguy, I did read the manual, but obviously didn't recall all the details - there's a lot going on with this car ;)

Like I said, I've disengaged the AP when I get outside my comfort zone, and I'm always paying attention, so I'm not really worried that it's going to kill me. Just wanted to hear from others' experience, though you are probably right in that I should have gone back for a 2nd reading of the manual before posting.

As for AP being for freeways only, I could see this applying on freeways where you come up quickly on stopped (or very slow) traffic, I just haven't had that scenario play out yet.

Daryl | 17 April 2019

The manual may officially say that AP is for freeways only, but Musk has said that it can be enabled on any roadway that has lane markers. Some of us like to push the envelope, and so, taking this question in that spirit:

I have often felt nervous coming up on cars stopped for a light, especially coming around a curve. I definitely do not completely trust the car to stop, but in my experience the car has always seen the stopped traffic in time to stop.
However, it often waits longer and then stops a lot more abruptly than I would and I get pretty nervous with my foot poised over the brake pedal.

So my own philosophy is to test it and see where it works and how, but to always be prepared to take over.

When my car was new about a year ago, Autopilot would only engage on divided highways. Since then it has started working on city streets. I'm sure that Tesla is collecting data about how well it works in the city, but they can't officially support it's use there yet.

Also consider the fact that the "red light warning" feature they just implemented only works if you have AP engaged on city streets where there are stop lights. Again, another clue that they are expecting people to engage AP on city streets.

bruryan | 17 April 2019

I often drive on city streets and roads that are modified highways. You are observing something I have found also. IF the line of stopped cars at a light is not more or less directly in front of the car it will not see around a corner or hill. The car will come to a stop when it becomes aware of the situation but by that time my internal clock has run out and I've disengaged.
This may be an issue Tesla will never beat. There are cases where the lights are hard enough for local drivers to decipher from a distance.

BobDobbs | 17 April 2019

If "AP is for freeways only" as is the common mantra here, then why have they rolled out a feature that warns you that you are going to run a red light when on AP?

There's a huge difference between city driving and 60 MPH highways with occasional lights with respect to AP safety, and I don't see that being recognized by the "you're crazy and going to die if you use AP with stop lights" crowd.

M3phan | 17 April 2019

What’s your car distance setting at?

walnotr | 17 April 2019

I have yet to have a red light warning but I’m the guy that stops when the light turns yellow. I have pushed it a couple of times and have not received a warning yet. It might be working for some of the early access folks but not for us “others”. There is a YouTube video out there where the driver lets the car go as far as possible without hitting the brakes and never gets a warning.

pyee78 | 17 April 2019

@M3phan, typically 3 cars is what I leave the follow distance on. I've reduced it to 1 in very slow stop and go traffic to try and limit people behind me getting frustrated, but any time traffic is moving at posted speeds I set it to 3.

Seth.e.levine | 17 April 2019

M3phan has a good point, if you set the following distance to 4 or 5 you may notice that the response is quicker.

M3phan | 17 April 2019

Worth a try

TexasBob | 17 April 2019

To be fair to OP, I looked it up and manual now says "Autosteer is intended for use only on highways and limited-access roads with a fully attentive driver." So they have expanded the envelop from limited access to highways AND limited-access.

I would not do it but manual says... so

Hal Fisher | 17 April 2019

Instead of turning off ap you can adjust the max speed down using the right thumbwheel. Set it to like 30 mph when you see stopped traffic ahead and it will have time to break. Then just spin back up to increase when clear.

jjgunn | 17 April 2019

Don't take chances. Always err on the side of caution & drive defensively.

Please don't take any chances, get in an accident & ruin it for the rest of us.

You are 100% in control of your vehicle, 100% of the time.

surfpearl | 18 April 2019

I use AP on city streets as well as highways and freeways (am aware what the manual says). Works very well for me since I'm observant and know its limitations. Follow distance set to 7 and speed limit offset to 0. It detects stopped traffic in my lane of travel, no problem. The only difficulty is when I drive in the right-most lane while there are vehicles parked on the right hand side of the road where the road also happens to curve to the right. It freaks out and brakes for those parked cars, but I anticipate that and either change lanes or disengage AP in advance of those situations.

phinallydone03 | 18 April 2019

Never get warning! Even speed up at red light. Scary.

@Surfpearl, I have experienced those situations. I hardly disengage AP when it freaks out and brakes. Instead, I put gas pedal so that it won't stop immediately (I always afraid someone will hit me from behind when the car freaks out). After it passes, take off the gas pedal and AP resumes. Hope it makes sense!

Wormtown Kris | 18 April 2019

Question: Would it be valid/ constructive for the OP to issue a bug report when this occurs? "Bug report: As I came up to this stopped traffic at a red light, this is what is happening and I am concerned...." It's NOT technically a bug, but could it be helpful to flag an "edge case" scenario that is making users uneasy? The reviewers can watch back the camera and internal AP data and see if it is reacting properly in these instances?

parmesan | 18 April 2019


I drive it on a highway everyday with a 55mph speedlimit. Mine is a straight road with ~6 lights. I have noticed that AP does not slow down at the same time that I would have. 8 out of 10 times i take control. I have tried a few different car lengths. So not sure if the curvature of the road has anything do with it. Note that there is a concrete divider b/w me and oncoming traffic, so i think this is safe.Another problem is when the light turns green, AP is slow to accelerate .

walnotr | 18 April 2019

Folks, AP is still a driver assist feature. Just as the original cruise control would run you into the car ahead of you, AP has limitations. Knowing those limitations is the driver’s responsibility and there is a learning curve involved. That learning comes from finding your comfort level in various situations encountered while using it. The car does not drive like you or I do. Over time, the trust level increases as the car handles various situations competently.

Donz_S | 18 April 2019

Good inputs!

@walnotr: Almost my first outing after getting 2019.8.5, I encountered the red light alert. In my case, as I approached the already red light (using NoA), with no other vehicles around at all, the loud warning chime when off. "That" startled me more than anything since I was already anticipating to slow and stop for the upcoming light. :-)

@Hal Fisher: I do precisely that... A quick down scroll reduces the speed to be much more like my driving style rather than any notion of partial or hard breaking.

pyee78 | 18 April 2019

@Hal Fisher - good idea with the "scroll braking" Pretty effective slowdown without fully disrupting AP.

For everyone worried about me pushing envelopes, believe it or not, I want to be in an accident even less than you want me to be in one. I'm posting here to see what others' experiences are, because we can learn as a group faster than we can as individuals. I think it's also good for Tesla reps to hear how we're wanting to use these features, the challenges we're facing, and how we're working around them.

M3BlueGeorgia | 18 April 2019

In my experience it will eventually realize it is approaching stopped cars and stop.

But at 50 or 60 mph, that decision usually occurs too late for my comfort level and I touch the brakes to switch on regen and switch off cruise. :-)

Once the car shows the cars ahead on the display, you can switch back on cruise and let it take back over.

surfpearl | 19 April 2019

@phinallydone03 - It all makes sense, except the gas pedal :)

Marzipan | 19 April 2019

I had that happen on the highway two days after taking delivery - fairly sharp curve, traffic stopped right around the corner. Not sure if the car would have stopped by itself, I took over and all was good.

lupejerry | 19 April 2019

I had to bail out of AP yesterday because it seemed like it wasn't going to stop for the stopped traffic in front of me. Pretty scary situation, I was waiting on it to slow and stop and it just kept going, had to slam on the brakes.

CharleyBC | 19 April 2019

Even if we restrict the conversation to freeways for a moment, I’ve had interesting results with TACC. If I’m in the midst of traffic that is speeding up and slowing down and even stopping, I’ve found TACC to perform very well. As many have observed, it’s a big stress reliever in such traffic.

Where TACC has scared me is when I’m rolling along at the speed limit and am just approaching the back of the pack of stop and go traffic. As a human, I see the 5 mph traffic in front of me, and I’d start bleeding off speed so that I arrive at the back of the pack at an appropriate pace. But TACC will keep roaring along to the point where it worries me, and may well be frightening the driver ahead if she happens to be checking her mirrors. I end up taking over, not being willing to see what the outcome would be.

Clearly situations like this and the one the OP mentioned need to get more programming love before FSD becomes real. In the meantime, as we all know, pay attention and be prepared to take over.

suddled | 19 April 2019

@ Walnotr "I have yet to have a red light warning but I’m the guy that stops when the light turns yellow" You know that's not how the rules of road go right? You stop at RED lights not yellow...You are actually obligated to continue through an intersection on a yellow light. Future thanks from all the drivers behind you!

majassow | 19 April 2019

Well, I guess the rules depend on the location. Here in CA, you need to be out of the intersection before it turns red.
Of course, different lights have different yellow durations, so you can't count on a leasurly yellow. If you can comfortably stop when you see the yellow, you should. If it would be an uncomfortable stop, proceed. If you proceed and it turns red while you are in the intersection you we're probably travelling too fast (or, I guess: not fast enough -- depending on your driving style :-) ). Obviously, if there is congestion which prevents you from clearing the intersection, you must stop even on a green.

In Boston the rule is: it's not red until the first car stops.

CharleyBC | 19 April 2019

I still remember what they taught us in driver’s ed in Virginia: yellow means, “stop if safe to do so.”

Tronguy | 19 April 2019

All right, guys, here's the skinny, straight from the Collision Avoidance Assist section in the owner's manual. Complete with little red warning triangles all over.
The camera(s) and sensors associated with Forward Collsion Warning are designed to monitor an approximate area of up to 525 feet (160 meters) in your driving path. (snip some more).
- At 60 mph, that's about 88 feet per second. It takes 130 feet or so to stop from 60, so the autopilot has to respond within (520-130/88 = 4.4 seconds. Um #1.
Forward Collision Warning is designed only to provide visual and audible alerts. It does not attempt to apply the brakes or decelerate Model 3.
And, here's the big kicker. Under Autopilot, we have the fateful words:
Traffic-Aware Cruise Control cannot detect all objects and, especially in situations where you are driving over 50 mph (80 km/h) may not brake/decelerate when a vehicle or object is only partially in the driving lane or when the vehicle you are following moves out of your driving path and a stationary or slow-moving vehile or object is in front of you. Always pay attention to the road ahead and tay prepared to take immediate corrective action. Depending on Traffic-Aware Cruise Control to avoid a collision can result in serious injury or death. (snippage).
And _that's_ the part I was talking about.
OK, I admit it: There was a long article in ARS Technica that talked about traffic-aware cruise controls, not just in Tesla (although they talked quite a bit about it) but in other automobiles as well. See:
I had read that article some time before my wife and I took possession of our M3 LR so, naturally, went looking for details in the M3 User's Manual. And, yep, there it was: The car (like many cars that have traffic aware cruise control) has Issues with stopped objects. Like other cars. When the difference in speed is 50 mph or more. Sound familiar?
There's technical, engineering trade off issues here. For one thing, the radar in the cars looks not just at the time-of-flight to get distance, it also looks at the Doppler shift to get relative speed. Fundamentally, one sends out a pulse using a local signal; the reflection comes back at the radar signal frequency, and is mixed with the transmit frequency. That "mix" results in four products: A signal with the addition of the two frequencies (which, in this case, is roughly 2X the radar frequency); the original two frequencies (the radar frequency and the very-close Doppler-shifted radar return frequency), and the difference between the two frequencies (which will be Radar_Frquency - (Radar_Frequency + Doppler Shift) = Doppler Shifted Frequency. The Doppler shifted frequency goes up with closing speed: Hello, Police radars!. In the interests of Not Seeing Every Tree, Guardrail, Car Coming The Other Way, And All That Jazz (technically called "clutter), radar manufacturers put a low-pass filter on the mixer output, killing speed differences above 50 mph, as noted in the Tesla manual.
Which means the _car_ _is_ _blind_ to closing speeds faster than 50 mph or so.
As regards that 525 foot distance: I used to work on no-kidding airborne search radars. We could detect stuff 400 miles away (at altitude). We also had peak transmit powers around a megawatt or so which could fry nearby seagulls, the most sensitive receivers known to military contractors that your government could buy, and Big Antennas. Those milliwatt radar transmitters with consumer-grade receivers and The World's Dinkiest Antennas simply don't have the range.
Moral: Don't trust autopilot to detect a stopped car, fixed object, or a car coming the other way if the closing speed is more than 50 mph. READ THE MANUAL!!!!!

Reflex | 19 April 2019

@ majassow -- in California you need to be INTO the intersection before the light turns red, not OUT of it; I'm not a lawyer or cop, but I suspect that's the case in most of our united states.

Andres67 | 19 April 2019

@Pyee78, what I do in your scenario, so I don't have to disengage EAP, is use the right scroll ball to slow down. Then I'm going at a slower speed and the breaking is not abrupt when it finally senses the cars in front.

I'm sure it will just get better at recognizing these scenarios over time.

CharleyBC | 20 April 2019

@Tronguy: Nice education from an expert—thanks!

Whenever I learn about some engineering limit like this, I tend to ask, “how does this play out for FSD?” So in this case that we’re discussing, if radar has limitations where relative velocity exceeds 50 mph, how will level 4 or 5 autonomy be able to stop the car safely in the sorts of scenarios we’re kicking around in this thread? I clearly don’t know the answer, but I do know it’s a problem that must be solved.

Tronguy | 20 April 2019

@CharleyBC: And, if you read that Arstechnica article, the relationship between FSD and all this stuff is mentioned.
Basic point: It is possible to get around and Not Run Into Things without radar. _We_ do that, with a pair of crappy cameras for eyeballs. (Our eyes, as cameras, generally suck. With the exception, as far as I know, better light intensity range than film/CCDs.) What we have backing up those crappy cameras is some serious computational neural network chops inside our skulls, right along with eons of evolution with dead bodies all around where a computational failure to detect a tree in front of one at speed has been Removed via Darwin. Every once in a while I hear some specialized biologist describe How The Brain Does It; I generally get lost at the second turn where the field of view is autonomously separated into 5-point pentagons. Throw in more stuff, like the fact that the retina vibrates at a microscopic level somewhere around 100 Hz or so in order to get more detail and it all sounds (a) amazing and (b) the product of, literally, a billion years of incremental improvements, driven by (a) avoiding tigers in the underbrush and (b) finding food that doesn't want to be found.
In principle, then, all those cameras plotched around the car plus the about-to-be-delivered-and-used fancy new neural computer may actually be good enough to get us up to Level 5, or whatever Musk is calling FSD these days. My congrats to the Tesla Engineers if they can recapitulate a zillion years of evolution in their labs; this is not a task for the faint of heart.
Obligatory xkcd reference:

walnotr | 20 April 2019

@suddled - you misunderstand my point. When I said I stop for yellow lights, I mean when I’m approaching an intersection and the light turns yellow AND I can safely come to a stop, I do. I don’t believe when 2-3 seconds (about the length of the typical yellow) away from an intersection it means to floor it to make it into the intersection before the light turns red. I am constantly judging the distance and have a do not proceed line I will not cross if the light turns yellow before then. If I have crossed that line before the yellow, I go through. It’s all about defensive driving. I must be working for me because in 53 years of driving the insurance companies have not had to pay out any of the money I have given them.

walnotr | 20 April 2019

Ok, I was a little short on my yellow light timing. The same principle applies though.

The Federal Highway Administration's Manual on Uniform Traffic Control Devices provides guidance that the yellow interval be between three and six seconds without tying the requirement to specific approach velocities. That said, anything falling below the yellow times shown here should be considered as a potential short yellow light.
25 MPH -- 3.0 Seconds
30 MPH -- 3.5 Seconds
35 MPH -- 4.0 Seconds
40 MPH -- 4.5 Seconds
45 MPH -- 5.0 Seconds
50 MPH -- 5.5 Seconds
55 MPH -- 6.0 Seconds

styvwerx | 20 April 2019

I use NoA on the boulevards for cross town traffic sometimes, just for the sake of the data pool, and to see how it is progressing, but TACC much more often. I've encountered this issue, (rushing the stopped traffic beyond a safe stopping distance) on sweeper left turns so often that I know exactly when to tap the brake, and let re-gen slow me to a near stop. Sometimes I push the right wheel button and issue a bug report about it.

majassow | 20 April 2019

@reflex: I stand corrected.

Sparkylulu | 20 April 2019

I had to bail out of AP today in Los Angeles. 2 Weeks with the car, 10 times on this particular interchange with AP. Car handles perfectly each time it goes to take the ramp from one fwy to the other and this time, just as it was merging on to the off ramp I got a warning message that the AP would no longer be active and I had to take control. There was nothing in front of us, it was almost a straight line. Scared the bejeezus out of me.
Also, on another on-ramp, testing the AP's ability in downtown Los Angeles, the screen went blank and rebooted during the merge. I contacted Tesla and they said that they've had this reported and are working on an update. Anyone else experience these?

surfpearl | 21 April 2019

@Sparkylulu - Stay cool and be ready to take over from AP at any time, it's still in Beta.
As for the touchscreen, it's happening to a lot of us, see reports in other threads. No big deal, software fix is in the works, I'm sure.

Sparkylulu | 21 April 2019

Thanks, @Surfpearl. ALWAYS ready to take over. Since I live in LA I am very cautious. I've been driving here for 32 years and one thing you learn from AP and TACC is how awful those other drivers are. Drifting into lanes, cutting off, not paying attention, it's remarkable.
My hope is that my data helps Tesla improve, especially for this area. I has done remarkable well on one main Boulevard from the beach all the way to midtown, but, obviously, I had to remain in total control and ready.
Thanks for the encouraging words.