The fuel economy figures printed on a vehicle’s window sticker and in automaker advertising and brochures are estimates based on a test created by the Environmental Protection Agency (EPA). For each vehicle, there are two figures:
> City—represents urban driving, in which a vehicle is started in the morning and driven in stop-and-go rush-hour traffic.
> Highway—represents a mix of rural and interstate highway driving in a warmed-up vehicle, typical of longer trips in free-flowing traffic.
Based on dynamometer testing, these figures provide a way of comparing the gas mileage of different models. All EPA fuel-economy estimates can be accessed at fueleconomy.gov and they are also included on the ConsumerReports.org car model pages.
In Consumer Reports’ real-world fuel-economy testing, we’ve found that EPA estimates have typically been higher than you’re likely to get in normal driving. That’s why Consumer Reports conducts several different fuel-economy tests of their own, including separate city and highway driving loops. Vehicle speeds and atmospheric conditions are carefully monitored to ensure consistency. Fuel is measured by splicing a fuel meter into the vehicle’s fuel line.
The EPA revised its testing methods starting with the 2008 model year. Additional tests to account for faster speeds and acceleration, air-conditioner use, and colder outside temperatures have been added to the city and highway tests. The EPA has also said that mileage estimates have been adjusted downward to account for wind and road surface resistance, factors that can’t be replicated in the testing procedure.
Regardless of where the original figures come from, a vehicle’s fuel economy is not a constant or fixed number; it depends on driving styles and conditions, and will vary over time.
Article reprinted courtesy of Consumer Reports.