Poor emissions from cars that meet the latest European standards threaten to sabotage the effects of ultra-low emission zones such as that in place in central London, an independent emissions testing firm has said.

Ultra-low emissions zones generally see vehicles that fail to meet predetermined emissions standards charged to enter a given area of a town or city. In London, for example, petrol-powered cars must meet the Euro 4 emissions standard to avoid paying extra to enter the Congestion Charge zone, while diesel cars must meet the Euro 6 emissions standard. Those two levels have been chosen because meeting those standards requires a car to emit fewer than 80mg of nitrogen oxide (NOx) per kilometre travelled.

However, the Vehicle Market Surveillance Unit’s (VMSU) 2018 emissions testing programme, run by the Driver and Vehicle Standards Agency (DVSA), found that many diesel vehicles were emitting more NOx than they should have been on certain test cycles. The VMSU tested a range Euro 6-compliant vehicles in four different ways, using the old New European Driving Cycle (NEDC) hot and cold tests, as well as the new Worldwide Harmonised Light Vehicle Test Procedure (WLTP) cycle and the RDE (Real Driving Emissions) test.

Car dual exhaust pipe

All but two of the diesel cars tested - the Vauxhall Astra SRi and Volvo XC60 R-Design Lux D4 - met the required standard for the NEDC (cold) test at the first time of asking, although the Volvo was subsequently re-tested and found to be compliant. The Vauxhall, too, was re-tested, and passed the cold test second time around.

However, the RDE and WLTP tests proved more problematic for many of the vehicles. All but one model failed to meet the prescribed limit, while that car was joined by just two others in passing the RDE test. However, many of the vehicles tested were never designed to meet WLTP or RDE emissions requirements, and the VMSU has resolved to test some of the vehicles again.

Real World Emissions Testing

Despite this, though, the company behind a new independent emissions test called the AIR Index, says the results show using the Euro 6 standard as the basis for ULEZs will not stop “over-emitting cars adding to poor urban air quality”. One of the organisation’s founders, Nick Molden, said the VMSU research matched the AIR Index’s results and highlighted the need for independent testing.

“Cities who in good faith are using or plan to use Euro 6 as the threshold for access policies will not deliver the air quality improvements expected and will not solve their breach of urban air quality in the time required,” he said. “The DVSA’s latest test results confirm the importance of independent testing to provide confidence and transparency about actual emissions during on-road driving. We welcome the government’s publication of this report which aligns with the results of vehicles rated for the AIR Index, and it highlights again that not all Euro 6 cars control NOx emissions to the same degree.”

Diesel emissions