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Perils of Regenerative Braking

While all EV owners recognize that regenerative braking is one of the best forms of renewable energy, it also has down side that I would like to see addressed. I own a 2012 Chevrolet Volt and its Low gear uses a fairly aggressive form of regenerative braking, which got me to thinking…

In Normal mode Drive gear, the Volt’s regenerative braking seems about the same as an ICE car’s deceleration, but it feels a lot better because you know you’re recovering drive range every time you slow down.  That combined with knowing you’re losing no driving range when stopped takes all the sting out of stop lights.

So it was great when I discovered Normal mode Low gear and its highly aggressive regenerative braking.  Now even traffic jams are “fun” – I’m no longer driving slower than everyone else and every deceleration both uses regenerative braking and lets me practice traffic wave smoothing.

But I quickly realized that aggressive regenerative braking during traffic jams is a recipe for disaster, especially when the Volt’s brake lights do not come on, and everyone around you is bored, irritated, and easily distracted.

The more I thought about it, the more I realized that aggressive regenerative braking without automatically activating the car’s brake lights is very likely to increase rear-end collisions.

So I decided to try to do something about this by writing to my province’s Ministry of Transportation, the department responsible for traffic safety standards and vehicle safety specifications.  Below is the email I sent to them:

I believe there is a safety problem associated with the Ontario Highway Traffic Act and the use of brake lights, which while not critical now, is going to become increasingly severe as more and more electric vehicles are driving on our roads.   Please note that I am an electric vehicle owner (Chevrolet Volt 2012) and this problem is very concerning to me and the other Volt owners I have talked to.

Specifically, the Ontario Highway Traffic Act only requires the automatic application of a brake light when the “foot brake” is pressed.  Unfortunately, both electric and hybrid vehicles use regenerative braking which can significantly and quickly reduce the speed of a vehicle, but regenerative braking is controlled by the accelerator pedal, not the foot brake, so the “brake light” is never activated.

I predict that as hybrid and especially electric vehicle use rises, there is going to be a significant increase in rear-end collisions of vehicles making use of regenerative braking.   Regenerative braking will likely go unreported as the problem, because the driver behind will not be able to swear there were no brake lights on after he has hit the car in front of him.

I am not a lawyer, but from what I have read, here is the section that I believe needs changing:

From http://www.e-laws.gov.on.ca/html/statutes/english/elaws_statutes_90h08_e.htm#Top

Section 142(8)(b) states:(b) by means of a stop lamp or lamps on the rear of the vehicle which shall emit a red or amber light and which shall be actuated upon application of the service or foot brake and which may or may not be incorporated with one or more rear lamps. R.S.O. 1990, c. H.8, s. 142 (8).

My recommendation is to change 142(8)(b) to something like:

(b) by means of a stop lamp or lamps on the rear of the vehicle which shall emit a red or amber light and which shall be actuated whenever the vehicle is decelerating by more than 5 km/hour per second and which may or may not be incorporated with one or more rear lamps. R.S.O. 1990, c. H.8, s. 142 (8).

In other words, I recommend replacing “upon application of the service or foot brake” by “whenever the vehicle is decelerating by more than 5 km/hour per second“.

This way, regardless of why a vehicle is decelerating, provided it is decelerating past the defined threshold, the rear lights would come on, warning the following cars that this car is slowing down abruptly.   This would automatically cover:  brake pedal use, regenerative braking, engine braking, a change in road surface (like a switch to gravel) which suddenly decelerates the car, or even running into a obstacle such as a pile-up of cars.  Any of these situations would cause the rear lights to come on, warning the following cars of a potentially dangerous situation.

I would recommend this rule be made mandatory immediately for all new regenerative braking vehicles, and be phased in for all other vehicles over a fixed period of time, such as 5 years.

Note that the exact value of the deceleration threshold should not necessarily be 5 km/hour per second.  That value needs to be determined experimentally.

I hope you agree this suggestion has merit, and I would very much like to be kept apprised of the progress of this suggestion.

If I have not sent this suggestion to the correct email address, please let me know and I will forward this email appropriately.

Thank-you for your time,

Mark Batten-Carew

And the result of the above letter was this response:

Dear Mr. Batten-Carew,

Thank you very much for your e-mail addressed to Road Safety and Motor Vehicle Regulation Directorate of Transport Canada and conveying your concern regarding lack of a stop signal when activation of the regenerative braking system slows down the speed of a vehicle.

Under the Motor Vehicle Safety Act, Transport Canada develops and enforces the Canada Motor Vehicle Safety Standards (CMVSS). The Act requires that all new vehicles offered for sale in Canada be certified to comply with all safety regulations in effect at the time the main assembly of a vehicle is completed.

CMVSS 108 addresses lighting and light signalling devices installed on a vehicle. With regard to the stop lamp activation, CMVSS 108 requires that stop lamps are steady burning and they activate upon application of the service brakes; however, CMVSS 108 allows stop signal to be activated by a device designed to retard the motion of the vehicle. The discretion is left to the manufacturers who make the final decision as to what functions would provide added vehicle safety beyond the minimum safety requirements set by the federal regulations.

Transport Canada is not aware of any supporting data suggesting that the requirement for the illumination of stop lamps to indicate vehicle speed decrease caused by sole operation of the regenerative brake system would prevent rear end collisions. Nevertheless, the department monitors new technical developments and practicability and potential benefits of new safety measures. If it is demonstrated that a requirement for stricter rules regarding activation of stop signal would reduce road collisions in a cost-efficient manner, the department would consider amending the regulation.

Once again, thank you very much for sharing your concern.

Best regards

Marcin Gorzkowski,M.Eng., P. Eng.


My summary of the above letter is:

• Auto makers could do this if they wanted to,

• After-market products could be legally created and sold to do this, and

• No one has done a study proving this will be an issue, so they can’t just raise the bar in anticipation of the problem.

Well, hopefully I’ve planted the seed and someone will notice the correlation sooner or later.  Of course it’s not a big problem yet, since the ratio of electric cars is so small, but I think it will become one.

Please feel free to use my letter as a template to send to your state/province’s Ministry of Transportation.   Maybe if enough of us do it, it will come up as a topic of discussion at transportation conventions and the like. 

(This article was originally written as a Participant Blog entry in the Fleet Carma’s EV Champion Challenge, which has pulled together 4 teams of EV owners to see which of the Ford Focus Electric, Toyota Prius Plug-in, Nissan Leaf, or Chevrolet Volt comes out the best when driven by enthusiastic EV drivers doing their best to promote their own vehicle, but in real world conditions, not laboratory tests.)

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