WASHINGTON -- For all their performance prowess, Mercedes-Benz vehicles spend 23.9 percent of their time on the road idling, according to Daimler.
The company did that obscure bit of math in order to support a recent regulatory petition in which it's seeking to get better treatment under new U.S. fuel economy standards for its start-stop technology and other fuel-saving features.
The petition is a request for "off cycle" credits, which were added to the EPA's fuel economy program to recognize features that do not show up on the agency's standard fuel economy test cycle. Many features can qualify, including grille shutters that open and close to improve aerodynamics.
While environmental groups are somewhat skeptical of the program, for Mercedes, it's crucial to squeeze every last mile per gallon out of the off-cycle credits. In the past, the company simply paid fines to get around fuel economy mandates rather than meeting the efficiency goals. It was a cost of doing business for a brand whose core customers wanted big, powerful engines and were less concerned about saving money on gasoline.
Daimler paid 27 such fines to the U.S. government from the 1985 to 2011 model years totaling $349 million, records show; the rest of the auto industry paid a combined $495 million over that span.
But under the new standards, companies can no longer pay fines to comply. So Mercedes is now taking all the usual steps to improve fuel economy, including selling lighter cars with smaller engines and offering more efficient diesel, hybrid and electric powertrains.
William Craven, general manager of regulatory affairs at Daimler, said Mercedes will do what it takes to meet the standards. "I can tell you this with confidence," he said in an interview. "We're going to comply."
Petitions are also part of that plan. Mercedes' latest filing claims that it should get extra fuel economy credits because its start-stop system -- which automatically cuts off the engine when the driver comes to a stop at a red light or in traffic -- saves more fuel than regulators thought it would, for two reasons.
First, according to data Mercedes collected from insurance company Progressive, Mercedes vehicles idle more than the 13.76 percent of the time the EPA projected; Mercedes chalked that up to a conservative estimate by the EPA, but it may also reflect that Mercedes owners tend to live in urban and suburban areas. Second, Mercedes vehicles have an extra battery that lets the engine turn off for minutes at a time.
"There is a real savings here, and we have been able to definitively prove it," Craven said.
If the EPA goes along with the Mercedes proposal, which also seeks credits for ventilated seats, specially glazed windows and efficient lighting that the EPA acknowledges lessen fuel use, Mercedes cars would end up with about 5 percent better fuel economy in the agency's eyes, about 1 mpg more.
Craven said Mercedes will probably file more petitions in the future, including one for its crash-prevention features.
What's the connection? Fewer crashes mean fewer traffic jams, fewer cars starting and stopping and therefore, less gasoline wasted. Mercedes intends to make that argument with "guns a-blazing," Craven said.
Regulators are actually amenable to such arguments. They've decided to allow petitions to reward automakers for using technology that cuts pollution in the real world, said Margo Oge, who retired last year as head of the EPA's transportation office.
"We just want to make sure that the benefits are real," she said.
Other brands sell large cars with powerful engines, of course. But Mercedes has a tougher challenge than its competitors in meeting the EPA standards, which take into account a manufacturer's broad vehicle portfolio and sales volume.
Lexus, for example, gets leeway on fuel economy because sister brand Toyota sells the Prius hybrid in large volumes. BMW's big luxury cars are offset by Mini's miniaturized ones. Daimler does sell the tiny Smart ForTwo, but the 10,000 units it will sell in the United States this year are a drop in the bucket compared with the 300,000 that Mercedes is on pace to sell.
Daimler's passenger cars had a corporate average fuel economy of 30.2 mpg in the 2013 model year -- a gain of nearly 3 mpg from 2010, but still not enough to meet their 2013 target of 33.1 mpg, according to data from the National Highway Traffic Safety Administration. The automaker's light trucks followed a similar pattern. And the targets will only continue to rise through 2025.
Mercedes' petition is the first the EPA has considered since the new standards took effect for the 2012 model year. It is being warily watched by environmental groups, which worry about loopholes in the standards.
In comments to the EPA last week, environmental groups pointed out that Mercedes' start-stop system can be turned off with a button -- a choice Mercedes made to prevent the feature from annoying its drivers.
Even small credits make a big difference, said Dave Cooke, a vehicle analyst at the Union of Concerned Scientists. The 5 percent credit sought by Mercedes translates to about a ton of carbon dioxide kept out of the air over the life of a car.
"It's important that if we're giving them credit for a ton," Cooke said, "the real number isn't 500 pounds."
Other automakers didn't want to comment publicly on Mercedes' petition, but acknowledged privately that they are watching it with interest. They may decide to follow Mercedes if the EPA signs off on the start-stop request and sets a precedent, a senior fuel economy expert at a rival automaker said.
"Mercedes needs everything they can get, so they're trying to push the envelope here," the source said in an interview. "Whether more people follow suit will be determined by how the EPA reacts."