# Brake lights and Regen Braking



## 350VDC

Not sure if this was covered elsewhere, my apologies if it was.
I have been wondering if the brake lights come on when using regenerative braking and your foot is not on the brake pedal.
The reason is that the regen braking is awesome and slows the car down a lot, which is great for one pedal driving but what about the un-attentive driver behind you who doesnt have situational awareness of the traffic ahead and merely reacts to your brake lights?
So I decided to do a test tonight and am happy to say the Tesla Engineers have you covered. The Brake lights will come on when the regen is applied and the car slows down. Once the car is coasting at a constant speed the lights will turn off.
If you are using the low Regen setting, the brake lights do not come on immediately but only when the car starts to slow significantly. If you are going down a hill and the car is coasting at a constant speed, again the lights will go out.
I continue to love driving this car.


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## Rich M

You can see the little brake lights and turn signals light up on the on-screen car too. I don't know how much if any lag there is between the real brake lights and the on-screen representation.


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## JeopardE

Rich M said:


> You can see the little brake lights and turn signals light up on the on-screen car too. I don't know how much if any lag there is between the real brake lights and the on-screen representation.


Unless your car is MCR, in which case the onscreen brake lights are very hard to tell when they come on. Need to get Tesla to fix that!

I used the rear camera to check - there is no lag between the real brake lights and on-screen. Same with the blinkers. Perfectly synchronized.

I do have one other little pet peeve on this: you know how you use regen braking to slow down to a crawl, then finally transfer your foot to the brake pedal to halt? The brake lights don't stay on the whole time -- they turn off after the regen has tapered off and then they come back on when you hit the brake pedal. Car motion is smooth, but it must look weird to the person following - why do the brakes go on, off and on again? It nags me ... but maybe I'm just a little OCD about stuff like that.


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## CleanEV

I must be blind or otherwise colorblind. I cannot seem to see any indication of the little brake light mentioned by @Rich M.
I even recorded the drive and from the screen recording I was unable to make out where to see for those little lights. Maybe I need new pair of eyes:grinning:


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## Thunder7ga

I do see it on my screen.


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## Crouch

CleanEV said:


> I must be blind or otherwise colorblind. I cannot seem to see any indication of the little brake light mentioned by @Rich M.
> I even recorded the drive and from the screen recording I was unable to make out where to see for those little lights. Maybe I need new pair of eyes:grinning:


Since you own a red car you probably have a red car displayed on your screen so it will be near impossible to see the little red brake lights when they come on the display. I have a midnight silver displayed so it's easier to see the red lights (but still somewhat difficult) I have read on some forums that people with red cars have asked their service center to change the color of their displayed cars to something other than red to help with that issue.


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## raptor

I wish it was optional for regen to trigger the brake lights. Between Autopilot freaking out, aggressive braking behavior when speed limit changes while using TACC, and just trying to coast in general, other drivers must think I don't know how to drive.

There are a few other reasons, but it's something I miss from my LEAF driving days.


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## PNWmisty

raptor said:


> I wish it was optional for regen to trigger the brake lights. Between Autopilot freaking out, aggressive braking behavior when speed limit changes while using TACC, and just trying to coast in general, other drivers must think I don't know how to drive.


Federal regulations specify a rate of deceleration that must trigger the brake lights so it's not an option for Tesla to make it optional. And if you're just trying to coast but accidentally go into slight regen, that's not enough to trigger the brake lights so I don't think you need to worry about what other drivers think.


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## raptor

PNWmisty said:


> Federal regulations specify a rate of deceleration that must trigger the brake lights so it's not an option for Tesla to make it optional. And if you're just trying to coast but accidentally go into slight regen, that's not enough to trigger the brake lights so I don't think you need to worry about what other drivers think.


The LEAF doesn't trigger the brake lights, even at max regen (although it's only 30kW). Any idea what regulation this is, and if this would apply to manual transmission vehicles (mostly curious)?

It does feel embarrassing as it looks like I'm slamming the brakes when AP/TACC drops to follow new speed limit (e.g., 40->35).

Another guy did a 180 to follow me home, so I dropped my speed to 25 MPH (side road) hoping he would turn around before I hit my street, but I forgot about the brake lights, and of course, they turned on as I got close to my street and started slowing down from 25. He did another 180 right away, so hopefully he was just curious about the car, but the slow stalking behavior was odd.


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## PNWmisty

raptor said:


> The LEAF doesn't trigger the brake lights, even at max regen (although it's only 30kW). Any idea what regulation this is, and if this would apply to manual transmission vehicles (mostly curious)?


Manual and automatic transmission ICE vehicles are only required to illuminate brake lights when the brakes are activated. Since electric cars have regenerative braking, they have their own regulations.

https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R13hr2e.pdf

Look under UNECE 13H

5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:
Vehicle decelerations

Signal generation 
≤ 0.7 m/s² The signal shall not be generated 
> 0.7 m/s² and ≤ 1.3 m/s² The signal may be generated 
> 1.3 m/s² The signal shall be generated

In all cases the signal shall be de-activated at the latest when the deceleration has fallen below 0.7 m/s².



> It does feel embarrassing as it looks like I'm slamming the brakes when AP/TACC drops to follow new speed limit (e.g., 40->35).


I don't understand this. All vehicles brake lights come on when your foot touches the brake pedal, even if only applying the brakes very lightly.


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## CleanEV

@PNWmisty 
Interesting read


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## raptor

PNWmisty said:


> Manual and automatic transmission ICE vehicles are only required to illuminate brake lights when the brakes are activated. Since electric cars have regenerative braking, they have their own regulations.
> 
> https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R13hr2e.pdf
> 
> Look under UNECE 13H
> 
> 5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:
> Vehicle decelerations
> 
> Signal generation
> ≤ 0.7 m/s² The signal shall not be generated
> > 0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
> > 1.3 m/s² The signal shall be generated
> 
> In all cases the signal shall be de-activated at the latest when the deceleration has fallen below 0.7 m/s².
> 
> I don't understand this. All vehicles brake lights come on when your foot touches the brake pedal, even if only applying the brakes very lightly.


Thanks, that's the data I was looking for. It bothers me because my previous vehicle didn't do this, AP/TACC exuberates this, and it bothers me when people ride their brakes, or brake in the middle of nowhere. Now I'm one of them . Of course, this is a personal opinion/experience, and won't bother everyone.


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## John

When you use Autopilot, you start to notice that sometimes cars without brake lights on are slowing down, and sometimes cars with brake lights on are not. Autopilot relies on radar (currently), and just slows down when they actually slow down. Just interesting to note the exceptions to what you'd expect.


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## Bernard

Crouch said:


> Since you own a red car you probably have a red car displayed on your screen so it will be near impossible to see the little red brake lights when they come on the display. I have a midnight silver displayed so it's easier to see the red lights (but still somewhat difficult) I have read on some forums that people with red cars have asked their service center to change the color of their displayed cars to something other than red to help with that issue.


Can confirm it's just about impossible to see with a red car. Not that I need to see them light up, since I know it's happening.


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## Bernard

PNWmisty said:


> Manual and automatic transmission ICE vehicles are only required to illuminate brake lights when the brakes are activated. Since electric cars have regenerative braking, they have their own regulations.
> 
> https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R13hr2e.pdf
> 
> Look under UNECE 13H
> 
> 5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:
> Vehicle decelerations
> 
> Signal generation
> ≤ 0.7 m/s² The signal shall not be generated
> > 0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
> > 1.3 m/s² The signal shall be generated
> 
> In all cases the signal shall be de-activated at the latest when the deceleration has fallen below 0.7 m/s².
> 
> I don't understand this. All vehicles brake lights come on when your foot touches the brake pedal, even if only applying the brakes very lightly.


Not sure that the OP had in mind with the "embarrassed" statement, but I had the same feeling for the first few days of driving my Model 3, coming from a lifetime of using gearshift cars where braking is usually done by downshifting -- in Europe, someone who is showing brake lights every few seconds for this or that is considered a really bad driver, since one should downshift to take curves, to observe a lower speed limit, to slow down for a red light ahead, etc. Because brake lights in an ICE car come on only when the brake pedal is pushed, all of these decelerating actions through downshifting happen without any brake lights. (In the US, I'd do the same with an automatic car although it's much less smooth and much less useful without a clutch pedal, by using the shifter mode.)
Of course, unlike braking by regen, braking by downshifting does not save any energy -- just like braking with brakes, it just produces heat (although at least it does not produce brake pad powder); but it is the right way to drive a stickshift car, and the evidence to other drivers is the lack of flashing of braking lights. With an EV, using regen is much like a hugely improved form of downshifting (much more flexible and subtle, no matter how good one was with the clutch on an ICE car), but it produces a lot more brake light flashes. It will take European drivers some time to get accustomed to the idea that the driver of a car that shows braking lights for mundane tasks such as following speed limits or slowing down for curves is not necessarily a bad driver -- they may just be driving an EV ;-)


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## DannyHamilton

Bernard said:


> It will take European drivers some time to get accustomed to the idea that the driver of a car that shows braking lights for mundane tasks such as following speed limits or slowing down for curves is not necessarily a bad driver -- they may just be driving an EV ;-)


Whether the brake lights come on or not during regen appears to be a function of how quickly you are decelerating. If you just ease up on the accelerator pedal a bit to adjust for speed limits or curves, then the braking lights won't come on. If you are decelerating quickly, then it's probably a good idea to let the person behind you know that they'll be closing on you exceptionally quickly.


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## Polok

I used to follow the advice of this thread, but now I have second thoughts and switched my car to: low regen, creep mode on. 

Earlier this week, driving in the evening, I had been almost rear ended after using standard (full) regen to come to almost complete stop (<10 kmph) before making turn into a side road. I did some extra testing and I believe regen braking / brake light functionality is problematic. 

Brake light may turn on during _strong_ deceleration, but will turn off once car slows down significantly and rate of deceleration is low. You end up with almost stopped / very slow moving car with no brake lights on, which is technically correct, but will confuse average driver arriving behind you.

In same situation, a typical car (gasoline + automatic transmission) would be coasting on the brake, resulting in brake light on. Driver behind me was accustomed to typical behaviour. 

I am not really sure how Tesla can fix it, for now I switched creep mode to on and regen to low which forces me to apply the brake and turn on the brake light.

Of course it is only a problem in locations where vast majority of cars have automatic transmission and the drivers expect brake lights to come on 'generously'


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## garsh

Polok said:


> I am not really sure how Tesla can fix it...


Unfortunately, Tesla can't fix peoples' inability to pay attention.


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## Polok

I was thinking a bit more about it and a better brake light algorithm might be:
- to keep the brake light ON following a deceleration to a very low speed or stop 
- switch brake light OFF following acceleration

This would mimic more closely behaviour of a typical automatic transmission car, while still behaving reasonably in stop and go traffic.

I need to give credit to youtube user model3man, who created awesome video ( youtube: aijuAjxCZ7A) documenting how his model 3 was rear ended and sadly killed, during day time on a straight road. I am not sure what were his creep mode / regen settings, but having seen his the video a day before being nearly rear-ended got me think about it more.


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## ADK46

This is a choice the engineers may be getting wrong, generally, in my view: Do they want the car to do the logical thing, or do what (good) drivers usually do? Do they impose good engineering priniciples, or accept that it is dangerous to have the car doing things that will surprise ordinary drivers? On auto pilot, should the car go down the middle of the lane in curves, or hug the inside lane marker as nearly all drivers do? 

My opinion: All else being equal, the car should appear to be driven by a good human driver, whatever that is.


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## 30cl

Are the brake lights on during hard regen without brake pedal applied?
I am just constantly worried about the car behind me.


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## SoCalWine

For hard braking, yes. You can actually see the lights come on on the screen if you look close enough.

I had the same concern when I first started using TACC. Or even just how frequently the brake lights come on when regen.


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## Charlie W

Yes, they are on — and you can see them come on, on the picture of your car on the screen. They’re really tiny though.

~Charlie


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## RonAz

I like Europe's flashing brake lights during hard braking. One more additional message to the traffic behind them. As a truck driver I used this feature frequently by turning on four way flashers. I still do the same in my passenger vehicles. If you practice a bit, your hand will go to the correct switch without having to look.
I also am in favor of the rear fog light. Problem here is that Audi and Mercedes drivers don't know the have that feature, so it's on all the time.


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## RonAz

TriMet buses in Portland had a good feature for awhile. Mounted on the back was a strip with three lights in it. The green light was on it the bus was under power, the amber light light was on for coasting or engine braking, and the red light came on in addition to the standard brake lights to let you know that they were stopping. I don't think that it caught on though. I don't recall seeing it for awhile.


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