OPINION: A different perspective on regenerative braking

There has been some debate recently on various electric vehicle websites regarding the use of regenerative braking (a.k.a. regen) and one-pedal driving. Most of the comments have focused on issues such as convenience, the difficulty of learning a new driving technique, passenger comfort and so on. 

Many EVs allow the driver to select the strength of the regenerative braking. It is not uncommon for some EV owners to set the regen to its lowest level so that their car mimics the braking behavior of a typical ICE vehicle. I consider that to be a mistake and I would like to share a slightly different perspective on this topic.

I have been involved in emergency medical services for almost 30 years, including more than 20 years as a paramedic instructor. Like everyone else who works in a public safety profession, I have seen more than my fair share of injury and death. The most difficult calls always involve children, and I have responded to several incidents where a child has been struck by a vehicle, usually after the child ran out into the road without looking.

It is not an exaggeration to say that the difference between life and death in these instances is measured in milliseconds. 

If you are driving a typical ICE vehicle and a child runs out in front of you, your car will not slow down until you apply pressure to the brake pedal. During the time you are lifting your foot off the accelerator, moving it across from the accelerator to the brake pedal and beginning to press on the brake, your car is not slowing down in any significant way. 

Those are milliseconds that are lost at a time when you have none to spare.

However, if you are driving an EV with maximum regenerative braking, the moment you begin raising your foot off the accelerator your car starts to slow down. 

It continues to slow as your foot moves from the accelerator to the brake pedal. 

It continues to slow as you begin to push on the brake. 

By the time you have depressed the brake pedal enough to pressurize the hydraulic fluid in the lines and force the calipers and pads to begin squeezing the rotors, the speed of your car has already slowed appreciably due to the regenerative braking of the magnets in the electric motor.  

You might think this makes little difference in the “real world.” If so, please consider these facts.

A car traveling at 55 mph will cover 80.6 feet in one second. When an average driver decides to stop, it takes roughly 1.5 seconds to lift the foot upwards off the accelerator, move the foot laterally from the accelerator to the brake pedal and begin to press on the brake. Once the driver’s foot contacts the brake and begins to apply downward pressure, it takes another 0.3 seconds for the pads to make contact with the rotors (assuming a perfectly adjusted brake system).

In other words, from the moment the driver starts to lift his or her foot from the accelerator, a typical ICE car will travel 1.8 seconds before even beginning to slow down. That is a distance of 145.1 feet.

In an EV with the regenerative braking set at its maximum level, significant braking will begin instantly the moment the driver’s foot starts to lift upwards from the accelerator. This can make an enormous difference. 

Why? Because physics tells us that the energy at the moment of impact is most dependent upon speed. 

In the formula for kinetic energy (the energy of motion), velocity is squared. What this means is that by reducing the speed at impact by half, you reduce the impact energy by a factor of four! And that can be the difference between life and death.

You can drive with maximum regen and still drive smoothly. You simply need to slightly change the way you think about driving. 

You will soon learn that lifting your foot off the accelerator causes your car to slow down as if you were pressing on the brake. If you jerk your foot off the accelerator it will feel as though you just hit the brake. Therefore, to slow down and stop smoothly, you simply lift your foot slowly and smoothly off the accelerator. With a little practice, your passengers won’t feel any difference.

I encourage you to drive your EV with maximum regenerative braking. This is a superpower that your EV possesses! Please use it.

Read more about what Marty Young Loves about his EV.

Marty Young is an Associate Professor of Emergency Medical Services at the Roane State Community College Center for Health Sciences in Knoxville, Tennessee.