The tests were carried out on 56 vehicles in Germany and 37 in the UK, with the sample targeted at a 75% spread of the top 100 best-selling diesel models of recent years, representing more than 50% of diesels on UK roads, powered by both Euro 5 and Euro 6 compliant engines. Non-VW vehicles included the Ford Focus, BMW 3 Series, Jaguar XE, Nissan Qashqai, Vauxhall Astra and Volvo V40. The government estimates the test programme cost tax payers £1m.
The cars were sourced from car hire fleets and had covered no more than 30,000 miles to ensure that they could not have been interfered with and were in good mechanical condition, a move taken after accusations has been made that car makers were submitting optimised cars for official tests. They were all fuelled by the same batch of diesel.
However, while all cars met the legally required levels of emissions in lab tests, real-world testing on track, particularly when the cars were tested with the engines pre-warmed, resulted in NOx emissions on average five times higher than those recorded with the engines pre-warmed in lab tests for Euro 5 engines and 4.5 times higher for Euro 6 engines.
In particular, exhaust gas recirculation (EGR) systems came in for scrutiny, and particularly the fact that manufacturers legally alter the level of EGR according to ambient conditions in order to ensure the longevity of parts. While this is legal, Department for Transport officials described the gap between lab and real-world results as "surprising" and highlighted that the loophole presented by allowing selective EGR use to extend parts life was being closed by changing regulations.
Transport secretary Patrick McLoughlin concluded: “Following the Volkswagen emissions scandal, the whole of the automotive industry must work hard to restore public trust by being transparent about the systems they employ and advancing plans for introducing cleaner engine technology.”
Goodwill added: “I’m disappointed that the results are as bad as they are in the real world. Our real-world tests have shown that the cars are not as clean as we thought. It is up to the industry now to meet the RDE standards, that we have been pushing hard for over some years. It is clear from the range of results that the industry can do better, and the new regulations will ensure than they will.”
Responding to the government's findings, the Society of Motor Manufacturers and Traders (SMMT), which represents the views of the motor industry, said: "What is immediately clear is that the vehicles tested met the legal standards with no new evidence that any other manufacturer has used any kind of lab cycle test recognition technology.
"The differences between the results from official laboratory tests and those performed in the 'real world' are well known, and [the] industry acknowledges the need for fundamental reform of the current test regime, which does it no favours."
Commenting on the introduction of the RDE test in Europe, the SMMT said the changes would "require signficant additional investment by manufacturers, but will add greater transparency so consumers can be more confident [the] industry is delivering on air quality while providing ever greater choice."
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