A campaign group said automakers should explain why new cars in Europe have CO2 emissions on the road that are far higher than laboratory tests show.
The gap between published specifications for fuel use and CO2 emissions and actual numbers widened to an average 40 percent last year compared with 8 percent in 2001, an annual study by environmental group Transport & Environment (T&E) showed.
Volkswagen’s revelation last week that "defeat" software was used in diesel engines to pass U.S. emissions tests for nitrogen oxides has raised questions in Europe about the testing process for both nitrogen oxides and C02.
Greg Archer, clean vehicles manager at T&E, said the study had found no evidence of foul play by automakers. "The gap doesn't prove the existence of [defeat device] software,” he said. “But the gaps of some of the results are so large that they are hard to explain. We don't have proof of defeat devices. What we do have is very suspicious data. We think it’s important that vehicle manufacturers tell the approval authorities why this is so."
Mercedes-Benz topped T&E's list of carmakers who overstate fuel economy for the second year in a row. Vehicles built by Mercedes used 48 percent more fuel on average than their published statistics claim, with gaps exceeding 50 percent on new A-, C- and E-class models, T&E said in a statement on Monday.
The BMW 5 series and the Peugeot 308 produced differences between real-world and laboratory results of just under 50 percent. The Renault Twingo had the smallest gap between real-world performance and road tests at about 10 percent. The VW Golf, Europe’s top-selling model, had a gap of about 40 percent.
The difference between published specifications and actual fuel use costing a typical driver an additional 450 euros ($500) yearly at the pump, T&E said. The group based its figures on a 600,000-car analysis compiled by the nonprofit International Council on Clean Transportation.
"Like the air-pollution tests, the European system of testing cars to measure fuel economy and carbon dioxide emissions is utterly discredited," Archer said a statement accompanying the study. "The Volkswagen scandal was just the tip of the iceberg."
T&E's report focused on fuel consumption and the CO2 emissions it implies. That's a different type of emissions than the nitrogen oxides, or NOx, that Volkswagen admitted to falsifying. Carbon dioxide is linked most strongly to global warming and not harmful for individuals, while other auto pollutants, such as NOx and fine particulates, can lead to respiratory diseases.
Daimler said that since T&E doesn't publish test conditions, "it’s not possible to properly examine" the results."Mercedes-Benz strongly supports the introduction of the so-called worldwide harmonized light-vehicles test procedure, so that test results from the lab and real road driving are closer together," Matthias Brock, a company spokesman, said.
PSA/Peugeot-Citroen supports the more stringent test results coming into effect in 2017, said Pierre-Olivier Salmon, a spokesman. The French carmaker posted some of the best results in an ICCT ranking of the divergence between on-road tests and official fuel consumption, Salmon said.
A BMW spokesman said: "It's not news that there are differences between lab tests and real-world results." The automaker "is adhering to the rules and regulations. We also support efforts to reform regulation in the EU designed to bring results closer in line with real-world driving conditions," he said.
The EU plans to replace the New European Driving Cycle (NEDC) test with a new Worldwide Harmonized Light Vehicles Test Procedure (WLTP) procedure for type approval in 2017. The new rules will require diesel vehicles sold under the latest Euro 6 air quality standard to undergo tests on roads rather than in laboratories.
The European Commission, the EU's executive arm, admits it has known for years of discrepancies between real-world driving and emissions levels in laboratories where new models of cars are tested for compliance with EU law. It says it outlawed defeat devices in 2007 and began work on improving testing procedures.
Bloomberg and Reuters contributed to this report