Safety and Regenerative Braking

Safety and Regenerative Braking

I figured this was worth it’s own post so here we are. I was wondering while driving, I have heard so many good things about the regenerative braking but then my mind started to question… things.

When you drive, or at least when I drive and I encounter heavy traffic, I find myself pumping the brakes to indicate to the cars coming behind me and coming at me really fast that traffic has come to a complete stop in order to notify them ahead of time not to rear-end me. Having 2 year old twins and knowing I will be getting the jump seats for them, the fear of them being back there and having other drivers plow into me is a real fear. There is no crumple zone back there as long as the front of the car of course and I know they will test and make sure it’s safe but worry and I still wonder about it.

Also, when you take your foot off the accelerator and the regenerative immediately triggers for the car to start slowing to a stop, does that also trigger the brake lights?

Tom A | 30. april 2012

If I recall correctly, the brake lights automatically turn on during regen in a Tesla. I don't remember where I read that. You might be able to find it in the Roadster blog or an old thread in this blog (Model S discussions). Search this site. I think you'll find the answer fairly quickly.

BYT | 30. april 2012

I found this article on the subject, and a quote: "Also, for those who wonder, the brake lights are computer controlled and based on measured deceleration rather than the standard switch on the brake pedal."

So then, when I want to signal the cars behind me that we are at a full stop or more accurately, coming to a full stop in this scenario, how to I make my brake lights flash to warn them?

EcLectric | 30. april 2012

The hazard indicators will work. They might get other drivers' attention better than brake lights.

BYT | 30. april 2012

It's an idea, but realistically I find myself pumping the brakes instinctively to notify others. Taking my hand of the wheel to hit the hazard lights doesn't sound like a good alternative to me. I know it sounds petty and like it's not a big deal, but when you are in traffic as much as I am and have so SO many close call's, I like to make sure others are also aware as I hate dealing with a rear ending (happens way too often to me). And again, with my really precious cargo in the jump seats, it's all the more critical for me.

jerry3 | 30. april 2012

When I drove the Land-Rover, the drill was you never used the brakes unless you absolutely had to. I never had any problems with people not being able to stop in time over almost 20 years of driving.

Sudre_ | 30. april 2012

I find that pumping the brakes makes absolutely no difference. I wonder if Mythbusters could test this one. Many if not most drivers will not notice you pumping your brakes. The best approach is to leave more distance in front of you so you can stop slower and move forward when that close call comes knocking. That way you are not relying on others as much.

If you are having issue getting rear ended or a lot of close calls it probably also indicates that brake pumping is not working.

ggr | 30. april 2012

The equivalent of pumping your brakes is simply to back off, and back on (to something around neutral) on the go pedal. It sounds hard but is completely intuitive.

BYT | 30. april 2012

I don't think I'm explaining the scenario well enough... :) If you are familiar with highway driving in the Bay Area or I imagine the same in L.A. then there are times (even keeping 4 or 5 seconds behind traffic in front of me) when traffic stops suddenly for many reasons. Other cars that maybe doing 65 to 85 MPH behind see the brake lights but misjudge the new rate of speed (how often have you seen someone veer off to the left or right of your car to avoid hitting you). I am not a sudden stopper by any stretch, just really unlucky I guess and spend a lot of time on the road. Brake pumping isn’t to stop the car but really to flash the brake lights so they know something is off and hope they don’t hit you.

People are people and they will make mistakes! I guess the real question is this: How well will the rear of the Model S hold up in a really bad rear-end collision with two little ones in the jump seats?

That's really all that matters or concerns me. No front crumple zone makes for a lower margin of preventing passengers from getting crushed back there.

Teoatawki | 30. april 2012

I believe the safety of the rear facing seats is maintained by being part of a cage that moves forward as a unit.

These back seats are possibly the safest seats in the Car, Tesla CEO Elon Musk said. And the Insurance Institute for Highway Safety agrees.

"If you're transporting kids, those rear-facing back seats would be the best place to put them," Insurance Institute spokesman Russ Rader said.

Not only are the children facing away from any likely frontal collision, the back end of the car is also reinforced to protect against high-speed rear-end impacts, even from large trucks.

The seats are equipped with racecar-type five-point harnesses, too.

Brian H | 01. kan 2012

Less fuss about actually using the belts, too. Which means no chance of kid-jectiles heading out thru the windshield in a front-ender.

Volker.Berlin | 02. kan 2012

BYT, I think I know what you mean and I have always been happy (and lucky) in these situations with flashing the hazard lights twice or thrice. I deliberately went away from pumping the brakes for the mere purpose of showing the brake lights, because it interferes with my own driving and the handling/stability of my own car. In an emergency situation the brakes should be "free" for me to use as is best for handling my car, and not be abused as a light switch. Just my 2c.

The issue of brake lights coming on upon heavy use of regenerative braking (without actually touching the brake pedal) has been discussed here:

It seems that the Roadster does show brake lights when decelerating above a certain rate even if the brake pedal is not touched. The behavior may be different in Europe, due to regulation which may require the brake lights to be tied exclusively to the physical brakes (regen is also a physical phenomenon, but you get the idea). I am not entirely sure though.

One thing I am sure about is that we cannot say anything about the Model S at this time. Tesla has been explicit that they redesigned/improved the behavior of the regenerative braking for the Model S (and has even announced that it will be driver-adjustable, though probably not in the very first versions, maybe upgrade-able later by way of firmware update).

I imagine that maybe the Model S will do some moderate regenerative braking on the release of the accelerator pedal, comparable to engine braking, and increase regenerative braking when the brake pedal is pushed, without immediately engaging the brake discs. But that's as good as anyones guess, and before going into any further detail I suggest everyone re-reads the thread linked above, because much of the discussion is already in there.

BYT | 02. kan 2012

Guess we wait and see, I also would love to see crash test results of rear collisions to put my mind at ease.

MandL | 03. kan 2012

The more traffic there is, the shorter following distance you have to keep in order to stay safe. People will constantly cut you off if you leave them enough room, and while they're trying to maneuver in front of you before their passing window closes, they're not noticing that the five cars already in front of you are braking, so they cut your following distance to nothing and then slam on the brakes.

I hope the external speaker on the Model S is a good one. I think I'm going to put a 120 dB tug boat whistle on my horn. :-)

BYT | 03. kan 2012

Electronic Blow Horn! I used to have a buddy who had a C.B. in his car with a P.A. option. We had a ton of fun with the P.A. in my teens until I told two older balding gentleman in an brown Lincoln Continental that Hair Club for Men were having a two for one special. After the contained their laughter, they placed a red light on top of the car and pulled us over.

Good Times!

stephen.kamichik | 03. kan 2012

I remember commenting to other driver's on the CB PA. Ah...youthful stupidity.

BYT | 04. kan 2012

Gives a storied to share later in life... ;) Also reminds us what we were like so we can tolerate or at least understand what our kids do later... hopefully!