Independent UK and German government testing has not uncovered any evidence of manufacturers other than the VW Group using defeat devices in emissions tests, but it has highlighted the gap between official laboratory test results and real-world emissions figures.
The Department for Transport report, revealed today, concluded that “existing lab tests designed to ensure emissions limits are met have been shown to be inadequate and this is why the UK has secured a tough new Europe-wide Real Driving Emissions (RDE) test”.
The RDE is set to be introduced in a staged process beginning next year and will include some real-world driving emissions measurements. Along with other emissions test and type approval changes, Europe's testing regime is set to be the toughest in the world by 2019.
Commenting on the confirmation that only VW Group cars were employing defeat devices in official NEDC emissions tests, transport minister Robert Goodwill said: “This finding is a significant step forward in assuring drivers that the serious breach of trust committed by Volkswagen is not more prevalent.”
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.