That new car probably isn't as green as you thought

Are new cars really producing less CO2 or have automakers mastered the test used to measure the "greenness" of their vehicles?

Jos Dings, director of Brussels-based green transport campaigners Transport & Environment, says that the official CO2 results given by the manufactures on cars sold in Europe "are less and less a reflection of what we are seeing on the road."

Dings says that there has always been a difference between the amount of CO2 a car emits during a controlled test and what it produces when actually driven. He said that gap used to be 20 percent but has risen to as high as 50 percent for models advertised as sub-100g/km cars.

"We don't want cuts on paper," Dings said in a phone interview. "We want them in reality."

Gareth Hession, who is vice president of research at JATO Dynamics, says no one can dispute that the additions of stop-start technology, downsized engines and better-rolling tires have helped cut CO2 in today's cars. However, he also is skeptical about the CO2 numbers derived from the tests.

Speaking from personal experience, Hession says he used to own a Mercedes-Benz E 220 diesel that had a reported CO2 level of 160g/km to 165g/km. The car's average UK fuel economy of 40 mpg (7.1 liters per 100km) meant the actual CO2 it produced was closer to 190g/km, according to conversion data. That's a difference of about 20 percent. Hession now drives a newer BMW 520 diesel. The car has a reported CO2 of 137g/km but he still gets about 40 mpg for the driving he does. That translates into roughly a 40 percent difference between the CO2 test result and reality. "I think there has been a lot learned on how to play the testing game," Hession says.

Sigrid de Vries, spokeswoman for European auto industry association ACEA, says that the current test – which dates back to the 1970s – does not factor in today's driving conditions, new technologies and other changes that have occurred over time.

"It does however present a way of comparison," de Vries said in an e-mail reply to questions. "It is in everyone's interest, and also the shared objective, that the new cycle would optimally represent as real conditions as possible."

De Vries added that the current test is up for revision. The aim is to have a global emissions test, but she concedes that making this happen has been a lengthy and difficult process.

Without an updated test for Europe, the automakers' published CO2 results become less believable every year. This is bad news for manufacturers, consumers and the environment.

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