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Are Other Automakers Cheating on Diesel? Not So Fast

Confusion over automobile emissions testing may be behind reports implying that that other manufacturers besides Volkswagen might be cheating.

In the wake of the Volkswagen diesel emissions scandal, a series of reports have suggested that other manufacturers might also be cheating, rigging their vehicles to do well on government tests while producing far more pollution in the real world.

So far no evidence has surfaced that other manufacturers have engaged in any similar subterfuge, but that fact has often been lost in reporting on the arcane science of automobile emissions testing.

For example, the latest article to drive down that road, a report Friday in British newspaper The Guardian, was headlined, “Four more carmakers join diesel emissions row.”

The article stated that diesel vehicles manufactured by Mercedes-Benz, Honda, Mazda and Mitsubishi emitted up to 20 times the smog-causing oxides of nitrogen, or NOx, as permitted by EU rules during real world testing by a U.K. lab. An earlier report by the Guardian cited similar tests by another lab as fingering diesels produced by Renault, Nissan, Hyundai, Citroen, Fiat, Volvo and Jeep for doing the same thing.

But Nick Molden, the CEO of Emissions Analytics, on whose data the Guardian relied, calling the report “rubbish.” The higher readings in real world testing are not a surprise and do not indicate that any of the manufacturers whose vehicles were tested did anything illegal, he said in an exclusive interview with TheDetroitBureau late Friday.

“They picked up the data … (and used it to) imply that four other manufacturers have been conducting illegal activities,” said Molden.

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To be fair, the Guardian article accurately noted that “no evidence of illegal activity, such as the ‘defeat devices’ used by Volkswagen,” has been uncovered among the other manufacturers.

The problem with such reporting, Molden and other experts say, is that it improperly conflates government emissions tests under tightly controlled lab conditions with the way vehicles are driven in the real world. The tests were never intended to reflect those real world conditions and standards developed for the lab are almost never achieved on city streets or highways, they say.

The European tests, in particular, don’t put a vehicle through the aggressive acceleration, uphill climbs and cold weather conditions a motorists is likely to experience – all of which would be expected to adversely affect emissions.

“You’ve got a very gentle test cycle with a lot of loopholes in it,” Molden said of the EU testing.

In reality, most diesel vehicles produce almost no NOx when the engine and emissions system have been warmed up and they’re cruising smoothly down a flat highway, Molden and other experts interviewed by said. But that changes when a driver is motoring aggressively or when adverse conditions are present, at times – briefly – producing to up to 20 times the supposed limit on unhealthful NOx.

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As a result, tests of about 200 diesel models have found that while the latest European standard permits the emission of 80 milligrams of NOx per kilometer, “On the road it will be four times the limit, or 320 mg,” said Molden, “and all legal.”

Arvind Thiruvengadam, a research professor at West Virginia University who helped uncover the Volkswagen cheating scheme, said the same is true in the U.S. “There would be differences between a certification test and a real world test,” he said. “I would be happy if a passenger car is putting out just five to six times the standard. But that would only be under extreme conditions. And cruising down the highway, I would expect to see it producing much less than the standard.”

Diesel engines, both researchers noted, are particularly vulnerable to emissions spikes, especially when it comes to nitrogen oxides. That has to do with the basic mechanics of the technology, a downside of the fact that diesels tend to deliver more torque, while also getting better mileage than comparable gasoline engines.

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The latest diesels – which use turbochargers, high-pressure injectors and urea injection systems – have seen major reductions in emissions, especially NOx and sooty particulates. In fact, British researcher Molden says five of the newest models, which he declined to identify, are matching lab and real-world emissions numbers.

Those more advanced emissions systems are just rolling out in Europe but are mandated here in the U.S. But even then, Thiruvengadam said, short emissions spikes will likely be the norm for diesels. What matters most, he said, is that, on the whole, they are much cleaner than ever.

The U.S. Environmental Protection Agency and California Air Resources Board are currently “in the process of testing all current model year light-duty diesel vehicle models” for model years 2015 and 2016, EPA spokeswoman Julia Valentine told She declined to provide details on those tests or describe how they are being conducted.

Both Thiruvengadam and Molden would like to see changes to emissions tests to make them better reflect real driving conditions. In addition to providing a more accurate pollution picture, they believe that revised testing would make it more difficult for a manufacturer, such as Volkswagen, that did try to cheat.

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