How is EPA Estimated Range Calculated?
When it comes to electric car specs, range is king. While car manufacturers can brag about horsepower numbers, 0-60 acceleration times, technology, and other amazing features, range is what gets the headlines with electric cars. EVs are still in their relative infancy and range numbers can make or break a new model’s commercial success.
In the U.S., the Environmental Protection Agency (EPA) is responsible for the efficiency ratings of all road-going vehicles – gasoline, hybrid, plug-in hybrid, electric, and everything in between. All electric cars certified for sale in America will therefore have an EPA-estimated range figure. This helps you to compare vehicles you may be considering.
If you’ve spent some time researching electric cars, especially on non-American websites, you might notice that the EPA’s range estimates for vehicles are typically lower than the same models in other markets. EPA’s metrics are a better representation of electric range in daily life than the “ideal” numbers quoted in Europe and other parts of the world.
How does the EPA calculate its estimated range? Read on to find out.
City And Highway Cycles
Much like with gasoline vehicles, the EPA has “city” and “highway” cycles for its electric vehicle testing, which simulate stop-and-go traffic as well as higher-speed cruising. Like with gasoline vehicles, the EPA conducts its testing on a dynamometer – also known as a “dyno” – and not actually out in the real world, where there are too many variables that can’t be controlled.
A dyno is a set of rollers on which a car can be “driven” while strapped into place in a static location. The dyno can help generate all kinds of data about a car from horsepower to fuel efficiency and can help calculate the electric range.
The EPA uses a carefully designed set of cycles which include speeding up, slowing down, stopping, and driving constantly at prescribed speeds. They run all cars through the same set of city and highway tests, and the two cycles are called the Urban Dynamometer Driving Schedule (UDDS) and the Highway Fuel Economy Driving Schedule (HWFET).
The UDDS simulates stop and go driving, with plenty of accelerating up to speed and breaking down to zero. The HWFET cycle simulates higher-speed highway driving by accelerating the vehicle up to speed, then speeding up and slowing down between 30 and 60 mph over the course of the test – no full stops. This is a closer simulation of highway conditions.
Conservative Real-World Estimates
Both the city and highway tests are conducted by the EPA starting with a full charge and after being parked overnight. A car is run successively between city and highway driving cycles until the battery is fully depleted and the car can’t go anymore. Then it is brought back to a full charge.
The EPA then calculates the vehicle’s energy consumption by dividing the kilowatt-hours of energy needed to fully charge the battery by the number of miles driven. The number of miles driven is used as the basis for determining the electric car’s estimated operating range.
The EPA multiplies its preliminary range numbers by 0.7 to account for different driving conditions and provide a “fudge factor” for electric car owners who might have to plan for charging up on a road trip. This means that the final range rating of a car has plenty of buffer. For example, the Tesla Model Y traveled 451 miles on the multi-cycle city/highway test procedure, but the EPA’s final range rating is 316 miles.
Remember that at the end of the day the EPA’s electric vehicle range ratings are just an estimate, just like its MPG ratings give you a sense of how efficient a gasoline car is. Your real range will depend on numerous driving conditions potentially including individual driving conditions, how aggressively you drive, and how hot or cold the weather is.
The good thing is that the EPA’s range estimates give you a consistent basis for comparing different electric cars and are one significant part of helping you find the right electric car for your needs.
