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Ever wonder what that sticker on the rear window of a new car is and where the information on it comes from? Here's everything you ever wanted to know, and more.

How The EPA Rates An Electric Car

Ever wonder what that sticker on the rear window of a new car is and where the information on it comes from? Here’s everything you ever wanted to know, and more.

People who are in the market for an electric car rely heavily on the ratings given to that particular make and model by the EPA. The range number is especially important. Even though it is calculated in a laboratory and may not reflect how far a real driver in the real world can go, it still provides a useful yardstick that allows shoppers to compare one electric car to another.

Range is just one of the pieces of information that appears on the Monroney sticker of every new car. That sticker is named for Senator Monroney of Oklahoma, who sponsored legislation in 1958 that required manufacturers to disclose the price of their cars. Since then, the sticker has added lots of other information considered important to shoppers.

So how does the EPA come up with those range numbers for EVs anyway? According to MyEV.com, each car is fully charged then left indoors overnight. The next day, it is placed on a dynamometer, which is sort of a treadmill for cars. Then it is run through a standard set of driving duties that simulate city or highway driving.

The city cycle models a typical rush hour commute with lots of stop and go driving and periods of idling. The highway protocol simulates driving on rural roads and interstate highways without any stops along the way. When the battery in the test car is depleted, it is brought back to a 100% state of charge and the amount of electricity required is carefully measured. Using a formula that equates the energy in one gallon of gasoline to 33.705 kilowatt hours of electricity, the EPA than calculates the MPGe — a measure of how efficient a car is.

At this moment in time, the Hyundai Ioniq battery electric car is the efficiency champion with a rating of 150 MPGe in city driving and 122 MPGe on the highway. The Tesla Model 3 Long Range is next at 136 MPGe city, 123 MPGe highway. For comparison purposes, the Chevy Bolt is rated 128 MPGe city and 11o MPGe highway.  The combined city/highway ratings are a weighted average in which the city number counts for 55% and the highway number counts for 45%.

The Monroney sticker for electric cars also lists how many kilowatt-hours of electricity it takes to drive 100 miles. The EPA says that number is actually a more accurate way of comparing electric vehicles one to the other.

It is important to keep in mind that all the information shown on the window sticker is derived under strictly controlled test conditions and may not match your experience in the real world. The laboratory where the tests are run is temperature- and humidity-controlled. Batteries are less efficient in cold and hot conditions. Higher speeds take more energy. If you drive 80 mph on the highway for long periods of time, your range will be significantly shorter than the highway rating for your model car.

Because it is conducted indoors, the highway test protocol eliminates the effect of wind resistance, further skewing the results. It also does not use the heater or air conditioner and is conducted with just the driver on board. All of those factors can significantly reduce range, so don’t expect your experience to be the same as the numbers derived from testing.

The Monroney sticker for an electric car contains two other bits of information that should be important to shoppers. The first is the estimated cost of electricity needed to drive 15,000 miles in a year. That information is then compared to the estimated cost of fuel for a conventional car over 5 years, resulting in a dollar amount that reflects how much a driver could save over that period of time. Usually it’s a pretty significant number.

Here’s an interesting tidbit. In the lower right corner of every Munroney sticker for an electric car is a QR code that can be scanned with a smartphone. It will take customers to a website where they can input information about their personal driving habits to get a better estimate of what their energy consumption and costs will be. The fueleconomy.gov website provides similar tools and is an excellent resource for comparing different models. It has information pertaining to all current and past electric, plug-in hybrid, and conventional cars.

So there you have it. Everything you always wanted to know about EPA ratings and Monroney stickers and more. Armed with this information, you will be better informed than most sales representatives at your local new car dealer.

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Written By

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else the Singularity may lead him. You can follow him on Twitter but not on any social media platforms run by evil overlords like Facebook.

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