Conventional vehicles powered by gasoline get better mileage on the highway than they do in the city, consuming more fuel per mile when forced to slow down, stop, and reaccelerate. Every time they brake to a halt, all of their momentum is lost and has to be restored by their internal combustion engines. Stopping completely again and again is extremely inefficient, and some momentum is wasted whenever they are forced to slow down. When travelling on the open road at higher velocities, wind resistance increases exponentially and undermines fuel economy in a different way, but the losses are not as great as those caused by repetitive braking and reacceleration. Electric vehicles use regenerative braking to improve the efficiency of stop and go driving, and the vast majority of them get better mileage in the city than they do on the highway.
Hybrids were the first passenger vehicles to deploy regenerative braking, and all electrified vehicles use the valuable technology to conserve fuel and mitigate greenhouse gas emissions. The electric motors in hybrids and fully electric vehicles can be configured to function as generators, harnessing the vehicle’s momentum and converting it into electricity that can then be stored in the battery. When the vehicle’s kinetic energy is used to spin the electric motor, physical resistance from the motor slows the vehicle and reduces the need to apply the conventional brakes. The regenerative braking system conserves a significant portion of the energy that would otherwise be wasted as frictional heat, making it available as supplemental electric fuel.
The deceleration associated with regenerative braking is felt when the driver lets up on the accelerator, and feels similar to the braking sensation experienced when downshifting a manual transmission. Many EV models provide a range of settings that allow the driver to adjust the strength of the regenerative braking system. A strong setting will deliver considerable braking without actually hitting the brakes and a weak setting will mimic the sensation of effortless coasting. Some EV models allow the driver to slow the vehicle to a complete stop without touching the brake pedal, a popular capability referred to as “one-pedal driving.” Regenerative braking systems are not strong enough to stop an EV quickly in an emergency, and all EVs have a normal brake pedal in the customary location that will slow the vehicle adequately whenever it is called upon.
Vehicles of all types incur fuel economy losses because of wind resistance, which is considerably stronger at highway velocities. Most folks understand that they will get better gas mileage if they slow down on the highway, but many choose to purchase however much fuel it takes to drive at a satisfying pace. For EV drivers, the tradeoff is not so simple. Limited driving range tends to be an issue when driving longer distances on the highway, creating an additional incentive to conserve fuel. The most efficient EVs are designed with exceptional aerodynamics to improve fuel economy at higher speeds, and virtually all EV dashboards provide a reliable estimate of the vehicle’s remaining range that increases when the driver slows down.
Regenerative braking makes a significant contribution to the overall efficiency of electrified vehicles and is designed for the hustle and bustle of city streets. The remarkable technology provides significant benefits to consumers and the environment, and will continue to be augmented by efforts to minimize wind resistance.
