EPA to re-evaluate rules for car mpg estimates

The U.S. government may change the rules for the gas mileage estimates that car buyers see on window stickers after finding that fuel economy figures for Ford's C-Max gas-electric hybrid car were inflated.

Discrepancies between advertised mileage ratings from the Environmental Protection Agency, which monitors mileage testing, and real-world mileage have affected a number of manufacturers, especially of hybrid vehicles. The EPA said Thursday it planned to update its fuel-economy labeling regulations, in part to address those issues.

The EPA's move follows Ford Motor Company's Thursday announcement that it will cut the C-Max's combined city-highway mileage estimate by nearly 9 percent to 43 mpg, down from 47 mpg, following complaints from consumers that the model's actual mileage fell short of claims. Ford will change the vehicle's window stickers to reflect the correct estimate and will reimburse customers who purchased a C-Max with a $550 check, while those who leased will receive $325.

The Ford case is the second in less than a year where an automaker has cut mileage estimates after an EPA investigation. In November, the EPA found inflated numbers on 13 Hyundai and Kia models, affecting 900,000 vehicles.

In the case of the C-Max, Ford followed EPA test procedures in calculating the mileage and did nothing wrong, said Christopher Grundler, the agency's director of transportation and air quality. The problem stemmed from agency guidelines that allow automakers to test one vehicle, then use its mileage estimates for other car models that have the same engines, transmissions and weight classifications, he said.

However, the EPA discovered that a test on one model may not be accurate for another because cars are getting increasingly more fuel-efficient.

Automakers follow EPA guidelines to do their own mileage tests, which are monitored by the agency. Experts say the Ford and Hyundai-Kia cases are signs that the EPA is getting more aggressive in verifying those tests.

The EPA began investigating the C-Max earlier this year after getting complaints from customers that actual mileage fell short of estimates. The initial estimates were high, Grundler said, because Ford tested the Fusion midsize hybrid, which has the same power system, and applied its mileage to the C-Max, he said.

However, the C-Max sits more upright and has different wheels and tires, so it doesn't slice through the wind as well as the Fusion, Grundler said. That caused the C-Max to show lower mileage when tested on its own.

In the past, similar vehicles powered by gas engines got similar mileage, so using one test for a family of vehicles worked well, Grundler said. But the single test doesn't work for more efficient models like hybrids, he said. Hybrids get better mileage than gas engines by using a combination of electric and gas motors.

"These differences are more pronounced when you have a vehicle that uses so little fuel," he said.

The current regulations were developed in 1977, and the EPA is asking for input before making changes.

The EPA's tests still measure gas mileage accurately, but the agency is studying them to make sure they keep up with fast-changing technology, Grundler said, adding that tests during the past six months show the window labels are accurate. "Most people are getting the label values," he said.

However, the consumer ratings website Consumer Reports tested the fuel economy of 315 cars in August and found that 55 percent of hybrid cars and 10 percent of conventional cars fell short of EPA fuel economy estimates by 10 percent or more.

"The largest differences involve some of the most fuel-­efficient cars, particularly hybrids," the report said. "So the people who care most about gas mileage could feel the most shortchanged."

Consumer Reports said last year that the Ford C-Max and Fusion hybrids fell about 20 percent short of their promised fuel economy in road tests.

The EPA on its website says its fuel-economy tests are "designed to reflect 'typical' driving conditions and driver behavior," but that its ratings "may not accurately predict" a vehicle's real-world mileage.

Al Jazeera and wire services