EPA's Outdated Process

The vast differences in driving conditions and the way people drive make it very difficult to establish a single fuel economy number for a specific vehicle. Some observers think we should ditch miles-per-gallon as the metric, and use gallons saved per 100 miles. The confusion over mileage measurement has left a lot of hybrid owners wondering what to do when the mileage doesn’t match the sticker.

EPA mileage numbers are inaccurately high for all cars, not just hybrids. The EPA test procedure, originally developed in late 1960s, is out of date. Today’s driving conditions are different:

  • We drive more on urban roadways
  • We get stuck in more traffic jams
  • We drive faster, increasing aerodynamic drag and decreasing efficiency

In 1985, the EPA tried to compensate for these differences by reducing the raw city figures by 10 percent and the highway figures by 22 percent, while keeping the test itself exactly the same. On Jan. 12, 2006, the Environmental Protection Agency announced that it—once again—plans to change how it calculates fuel economy for new cars and trucks to more accurately reflect the real-world mileage experience of American drivers. Consumers are likely to see lower, more accurate numbers on window stickers of model 2008 vehicles arriving in dealer showrooms in the fall of 2007.

The current city test is 11 miles and consists of 23 stops, with an average speed of 20 mph and about five minutes of idling. The 10-mile highway test includes no intermediate stops, minimal idling, and an average speed of 48 mph. Do you average 48 mph on the highway?

These conditions falsely inflate the mileage numbers for all cars, but the hybrid numbers may be even more inflated because:

  • Air-conditioning, which taxes the hybrid’s drivetrain, isn’t used in EPA testing.
  • The testing is done in moderate weather. Cold weather reduces the hybrid’s battery efficiency.
  • There are more variables in a hybrid’s fuel economy. Inconsistencies and inaccuracies over short test cycles can more dramatically misrepresent real-life numbers.

Motor Trend ran the hybrids through their own test procedure, tailored specifically to hybrids. Their figures came very close to EPA numbers, but still higher than the customer-reported real-world average numbers found on many Internet sites and discussion groups:

  • Mid-20s for all the SUV Hybrids and Honda Accord Hybrid
  • 40 mpg for the Honda Civic Hybrid
  • Mid-40s mpg for the Prius
  • 50 mpg for the Honda Insight

You may get more. You may get less. Hence, the term “YMMV,” which means "your mileage may vary."