"Over a year, this adds up to hundreds of dollars in more expensive fuel bills," said Matt Levey from Choice. About 11 million cars are affected by Volkswagen's emissions scandal. But are other carmarkers fudging their emissions figures as well? Volkswagen this month confessed to fitting devices into 11 million cars worldwide to cheat fuel emissions standards, including Audi and Skoda models. Its chief executive Martin Winterkorn stepped down and its market value went into freefall. Volkswagen's local arm is yet to reveal if any of the 50,000 local cars are affected. It is being probed by the Australian Competition and Consumer Commission to see whether it misled buyers and breached the law. Mr Levey said the Volkswagen scandal and Choice's results showed Australians could not trust the car industry to self-regulate.

Choice is calling for the government to enforce independent testing and on-road checking of manufacturers' questionable fuel usage and emissions claims. Danger of becoming 'dumping ground' for dirty cars It is also demanding Australia adopt compulsory standards for vehicle fuel efficiency and greenhouse emissions, so "we don't become a dumping ground for dirty, costly-to-run vehicles". "The industry says real-world tests are different to the laboratory. But new research from Europe shows the gap between car makers' claims and real-world performance keeps growing, and is now at 40 per cent," he said. "Australia is also the only advanced economy to have no compulsory standards for fuel efficiency or greenhouse emissions. In fact, in 2012, our average greenhouse emissions from new vehicles were 44 per cent higher than Europe."

Tony Weber, chief executive of the Federal Chamber of Automotive Industries, said manufacturers followed a government-set standard for measuring and reporting the fuel consumption of new light vehicles, which was based on definitions in the United Nations Regulation. He said results from laboratory tests could differ from user experience. "The test drive cycle may not be representative of their average driving environment. There may be more low-speed city driving over a longer distance than in the test, or when driving in summer, the air conditioning may be used," he said. "A lower specification fuel may be used. Or driver behaviour, such as the amount of equipment carried in the car, acceleration and braking habits [could result in different figures]." Independent Senator Nick Xenophon said he will introduce a private members bill in October that would impose harsh penalties of up to $50 million on car manufacturers which deliberately "game" the system.

At present, the Department of Infrastructure and Regional Development only conducts audits of car makers at random to test fuel consumption figures, and the only sanction available is for the ACCC to launch action for false and misleading conduct. "Car companies can use artificial test conditions, including taking out the back seats to make the car lighter or switching off features like air conditioning to make inaccurate fuel economy claims," said Mr Xenophon. "Testing for fuel economy can be difficult, but the gaps between what is advertised and what is actually achieved on the road really does stretch the credibility gap," he said. "A family could typically be many hundreds of dollars a year worse off from what they budgeted for because they've been misled into buying a particular car." Leading class action law firm Maurice Blackburn announced an investigation into a potential consumer law case against Volkswagen amid its global pollution rigging scandal.

The firm's class action principal Damian Scattini said the global test rigging scandal was likely to affect Australian car owners. "We believe that if it is confirmed that Australian cars are impacted then consumers may have grounds to take action against Volkswagen, including pushing for extended warranties given people as yet are still in the dark about the full impacts of this issue," he said.