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Why Do Hybrid Cars Get Such Great City Gas Mileage?

If you’re interested in buying a new car with a focus on fuel efficiency, you’ve probably noticed that most vehicles get better gas mileage on the highway than in the city. That makes sense; highway cruising usually requires less work than city driving. So, why do some hybrid cars get better fuel economy in the city than they do on the highway? Let us explain.

Fuel Economy Calculations

Before we cover the reason that hybrid vehicles get such excellent city fuel economy, it’s important to explain exactly how gas mileage is calculated. With today’s cars, three numbers make up a fuel economy rating: city mileage, highway mileage and combined mileage. The city rating primarily examines city driving patterns, factoring in stop-and-go traffic, low speeds and a small stint on the highway. Meanwhile, the highway rating consists of highway driving patterns, featuring primarily high-speed cruising with little stopping and starting.

The combined rating isn’t strictly a combination of the two. Rather, it’s an average that’s weighted a little more toward the city rating because most drivers spend more time in the city than on highways and rural roads.

Hybrid Cars and City Driving

Given that the city fuel economy ratings primarily involve low-speed and stop-and-go driving, it’s hard to imagine any car returning better gas mileage in the city than on the highway. But that’s exactly what happens with hybrids, largely thanks to a system called regenerative braking.

Regenerative braking is an energy-saving technology that hybrid vehicles have used since they first went on sale in the late 1990s. In essence, regenerative braking takes energy created during braking and harnesses it so the energy can be used for other purposes. In the case of many hybrid cars, this energy is sent back to the main battery, and that is used to power the car or extend the electric-only range, allowing the car to use less gasoline.

The result is that hybrid-car fuel efficiency actually improves when the car slows down. After all, the more stopping you do, the more electricity the hybrid can use to move the car forward. As a result, hybrid cars tend to offer slightly better gas mileage in the city because the low speed and increased braking mean more electricity and less gas are needed to power the car.

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3 COMMENTS

  1. “In essence, regenerative braking takes energy created during braking — usually in the form of heat — and harnesses it so the energy can be used for other purposes.”
    Umm, no. Existing regenerative braking uses the motor to convert kinetic energy (speed) into electricity.

    “In the case of many hybrid cars, this energy is used to power accessories, such as the radio and air conditioning. That means the engine is free to power the car’s actual driving process.”
    Again, no. The majority of the electricity is used by the motor to accelerate the car.

    “… the more stopping you do, the more energy your car can use to power accessories. The more regenerated energy the car uses to power accessories, the less engine power it must take away from the driving experience.”
    Who wrote this drivel? The general, most basic reason your car uses more energy the faster it goes is wind resistance. Hybrids allow enough energy to be captured and reused during slower city driving to more than offset the wind resistance of highway driving. Driving slower, around 40 MPH (less wind resistance) without having to stop (limited loss of kinetic energy) would get you the better mileage than either “city” or “highway” values.

    • It’s true, brakes capture kinetic energy, but the friction used to slow a vehicle produces heat. The original article made it seem like a hybrid captures lost heat, which it does not. We didn’t make a big deal about wind resistance because all cars have to overcome that, but the hybrid’s electric power is what really saves fuel in low-speed city driving. Makes us think hybrid drivers should be thankful for lots of traffic and low-speed commutes ; )

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Doug Demuro
Doug DeMuro writes articles and makes videos, mainly about cars. Doug was born in Denver, Colorado, and received an economics degree from Emory University in Atlanta. After graduation, Doug spent three years working for Porsche Cars North America. Eventually, he quit his job to become a writer, largely because it meant that he no longer had to wear pants. Doug’s work has been featured in a multitude of magazine publications and websites, including here at Autotrader — where he launched the Oversteer enthusiast blog — along with Jalopnik, GQ, and The Week. His YouTube channel has hundreds of published videos and has racked up hundreds of millions of views. Today, Doug lives in San Diego, California, with his 1997 Land Rover Defender 90 NAS, 2005 Ford GT, and 2012 Mercedes-Benz E63 AMG Wagon.

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