Autopilot stopping when light turns yellow?

[ahains]

Had autopilot on yesterday while driving on surface streets (hands on wheel, paying close attention), and I was surprised when it started to brake when a light turned yellow while approaching an intersection. There was plenty of time to get through the intersection before it turned red, so I immediately hit the accelerator. I was wondering if there had been something else near the car at that time that might also explain it, so I saved the dashcam footage to review later. It's not all that obvious, but you can see the image dip a very small amount at the exact moment the light turns yellow, and then back up as I hit the accelerator. I don't see anything else going on around the car, so it appears that it recognized the yellow light and hit the brakes. I'm not sure if it would have come to a full stop if I had not intervened. I believe I just hit the accelerator and did not disengage autopilot, but I don't remember for sure.

 

[SammichLover]

Had autopilot on yesterday while driving on surface streets (hands on wheel, paying close attention), and I was surprised when it started to brake when a light turned yellow while approaching an intersection. There was plenty of time to get through the intersection before it turned red, so I immediately hit the accelerator. I was wondering if there had been something else near the car at that time that might also explain it, so I saved the dashcam footage to review later. It's not all that obvious, but you can see the image dip a very small amount at the exact moment the light turns yellow, and then back up as I hit the accelerator. I don't see anything else going on around the car, so it appears that it recognized the yellow light and hit the brakes. I'm not sure if it would have come to a full stop if I had not intervened. I believe I just hit the accelerator and did not disengage autopilot, but I don't remember for sure.

It is possible the elevation change spooked it or you were close enough to the vehicle in front at it slowed slightly after passing the intersection and starting uphill.

 

[Kilotango74]

Well isn’t that what your supposed to do when presented with a yellow light....yield. How is the system supposed to know that there is “plenty of time before” the light turns red as there is no set time between yellow and red lights. Sometimes there is plenty and sometimes it’s ridiculously short depending on the particular intersection. I find that most people seem to just take the yellow light as an excuse to floor it, risking running a red light. In some states it is illegal to speed up through an intersection to avoid a red light. Don’t see Tesla programming the car to do this as running a red light would eventually happen. I guess people expect their autonomous car to drive with the same lack of concern for others as they do.

 

[SoManyM3s]

Well isn’t that what your supposed to do when presented with a yellow light....yield. How is the system supposed to know that there is “plenty of time before” the light turns red as there is no set time between yellow and red lights. Sometimes there is plenty and sometimes it’s ridiculously short depending on the particular intersection. I find that most people seem to just take the yellow light as an excuse to floor it, risking running a red light. In some states it is illegal to speed up through an intersection to avoid a red light. Don’t see Tesla programming the car to do this as running a red light would eventually happen. I guess people expect their autonomous car to drive with the same lack of concern for others as they do.

The car's not even supposed to be breaking for traffic lights right now. The point isn't that there was enough time. The point is that it braked

 

[AlanSubie4Life]

My guess is it thought the crosswalk was a disembodied semi trailer.

 

[Kilotango74]

The car's not even supposed to be breaking for traffic lights right now. The point isn't that there was enough time. The point is that it braked

Well AP is not “supposed” to be used on surface streets either so yeah. Big surprise another goofy response from a BETA system being used in a manner it wasn’t intended to be used in. Also you claim you had plenty of time to go through that intersection, but from what I can see in your post you must be used to running lots of red lights because that intersection is huge and you appear to be two car lengths from its beginning. But whatever just floor it right.....I mean I’m sure you were driving under the limit as you approached that intersection and accelerating wouldn’t have made you exceed to limit in a reckless manner in a crowded intersection right. But whatever. You keep on “testing” AP and just f$&k those of us driving and walking and biking around you right?

 

[SammichLover]

but from what I can see in your post you must be used to running lots of red lights because that intersection is huge and you appear to be two car lengths from its beginning.

I find it hard to judge distance from the car with that front camera, the angle and field view of the camera is such that you can't really judge the front of the vehicle directly, so I'm not sure exactly what the distance was and what it'd look like and how much room they had to brake in time, but they seem to have entered the intersection before the light turned red. If you're past the stop line prior to the red you aren't technically running it.

With the caveat that it isn't exactly clear when the vehicle braked and when the driver is overriding with the accelerator, because that telemetry isn't overlaid in the stock Model 3 camera footage;

Watching it again it really looks like the vehicle in front of them slowed, as the gap closed, so almost certainly TACC was reacting to traffic in front as intended. I can't really see the 2nd in-front vehicle at the end, if the vehicle in front closed that gap too then definitely TACC reacts to that. It adjusts follow distance not just on the first vehicle but another vehicle deep in front, and is pretty sensitive to speed delta changes going on. Which IMO is a very good thing.

 

[Kilotango74]

I find it hard to judge distance from the car with that front camera, the angle and field view of the camera is such that you can't really judge the front of the vehicle directly, so I'm not sure exactly what the distance was and what it'd look like and how much room they had to brake in time, but they seem to have entered the intersection before the light turned red. If you're past the stop line prior to the red you aren't technically running it.

Perhaps but it is illegal in a lot of places to accelerate through an intersection in order to avoid the red light.

 

[AlanSubie4Life]

Perhaps but it is illegal in a lot of places to accelerate through an intersection in order to avoid the red light.

There is no way the OP should have stopped...

In these videos it is really hard to perceive the speed. Until Tesla adds an overlay (if ever), you really have to have a marker and know the spacing and time. Looks like this was a 35mph limit area (I think that is what the sign on the far side says), so people were likely going 35-40.

I don’t think I would have even thought about stopping. The light turned yellow less than 1.4 seconds before entering the intersection. You can count the frames and estimate...

At 35mph, assuming the car did not slow (which it did), 1.4seconds would be 72ft. Since the car slowed, the actual distance when the light changed was less. Let’s say 65ft. (Visually inspecting the video, to me it looks like less than 65 feet based on estimating car lengths, but the videos can be deceiving.)

Human reaction time is about 250ms, when people are trying. That eats up another 10ft.

So 55ft from the intersection before even hitting the brakes is a possibility. You have to move your foot from accelerator to brake (though regen would start to slow you). It could easily be another 5 feet before really slamming the brake.

The emergency stopping distance with MXM4s from 35mph is (based on 60-0 in 125 ft):
d= v^2/(2a) = (35mph)^2/(2*9.44m/s^2)
= 42.5ft

To me, this is way too close. Basically an emergency stop would absolute best case leave you 12ft from the intersection (and maybe in the crosswalk).

Very likely to get rear ended stopping so abruptly.

but they seem to have entered the intersection before the light turned red.

Yes, they also seem to have exited the intersection before the light turned red!

 

[SammichLover]

Perhaps but it is illegal in a lot of places to accelerate through an intersection in order to avoid the red light.

They were countermanding AP, which had started to engage slowing.

 

[SammichLover]

Yes, they also seem to have exited the intersection before the light turned red!

Maybe, since you never see the red light come on in the video. I'm not sure about where the vertical field of view would put the vehicle when the traffic light structure moves off camera. But no way was it "running the red".

 

[Lloyd]

In most states, you are required to stop if you are able in the yellow.

 

[hcdavis3]

Perhaps but it is illegal in a lot of places to accelerate through an intersection in order to avoid the red light.

Here in MA Yellow light means floor it.

 

[SammichLover]

In most states, you are required to stop if you are able in the yellow.

And usually the lights are timed so there isn't really any meaningful distinction between the two, don't enter the intersection on a red and do stop for a yellow if you are able, at speed limit travel.

<edit> In fact one way to challenge a stop light ticket is to make sure the light's timing is such that the yellow is long enough to allow this, with appropriate time for human reaction time. Some jurisdictions actually do run their lights afoul of this.

 

[clostridium]

Well isn’t that what your supposed to do when presented with a yellow light....yield. How is the system supposed to know that there is “plenty of time before” the light turns red as there is no set time between yellow and red lights. Sometimes there is plenty and sometimes it’s ridiculously short depending on the particular intersection. I find that most people seem to just take the yellow light as an excuse to floor it, risking running a red light. In some states it is illegal to speed up through an intersection to avoid a red light. Don’t see Tesla programming the car to do this as running a red light would eventually happen. I guess people expect their autonomous car to drive with the same lack of concern for others as they do.

I agree that it is puzzling that it chose to brake at this intersection.

In response to some of the discussion about how the system would know when to brake: in the places I've driven the timing of the yellow lights is based on the speed limit on that street. I don't know if that is universally done or not. If it is then that provides the system with a pretty good way of making braking decisions. It knows how fast it is going, it knows the speed limit, it knows how long the light has been yellow, and it knows the distance to the intersection. That's all the variables to make a good decision.

I did find this interesting link discussing the tradeoffs between different lengths of yellow lights:
http://atsol.com/wp-content/uploads/2013/10/ATS-Yellow-Light-Time-Cutsheet-201309-v04.pdf

 

[clostridium]

In most states, you are required to stop if you are able in the yellow.

That is true in a number of states but I wouldn't characterize it as most states. It appears that at least half of states do not require you to stop on a yellow (of those some require it if pedestrians present though). This is based on a sampling of states on drivinglaws.org

The important point is that traffic laws vary state by state in sometimes unexpected ways. For example, it's strange that in Washington state you don't have to stop on a yellow but in Oregon you do. I'm sure that residents of Portland routinely cross over into Washington.

 

[AlanSubie4Life]

In most states, you are required to stop if you are able in the yellow.

That is true in a number of states but I wouldn't characterize it as most states.

Adding on to this, it is also probably not true as written in any state. There is an important word missing: safely

In states with restrictive yellow light laws, it is still logically intended to be (and usually written as such): “If you are able to stop safely”

I’ve been rear ended stopping for a yellow before (one I could have easily made it through safely), and my brother has had his car totaled before, when stopping abruptly for a yellow.

So, my rule now is to nearly always go - I just keep an eye on traffic ahead to be sure they are going as well. Generally I do not speed up to make it, unless I feel the person behind is following too closely. The purpose of a yellow light is to increase safety, so I try to behave in a way which improves safety - there are several factors that play into it. I do benefit from generally long yellow light timing in California, which makes it easier to make a safe decision one way or the other.

 

[Kilotango74]

They were countermanding AP, which had started to engage slowing.

So another reason not to be using AP on surface roads. “ But officer I was just cutting off my Auto pilot!”

 

[Kilotango74]

Here in MA Yellow light means floor it.

From my three year experience in MA so does a green light if you are making a left turn against traffic at an intersection. Don’t know how many times some masshole Floored it and cut right across my path when the light turned green. In fact we had a utility worker killed less than a block away from where we were living because of this action.

 

[brandonee916]

AP does NOT brake for lights at the moment, you can see that AP was braking due to the car in front of you with the elevation change it always thinks it's closer.