Consumer study finds 95% of diesels ‘break emissions limits’

Which? analysed data from more than 300 cars, and says vast majority break NOx limits in real-world conditions

Most diesel cars on UK roads produce levels of nitrogen oxide pollution which break legal limits when tested under real-world conditions, a consumer study of more than 300 cars found.

Which? testing found 95% of diesels emitted more NOx than permitted under EU regulations

Which? testing found 95% of diesels emitted more NOx than permitted under EU regulations

The results of a Which? study published today (January 20) show that 95% of the diesel cars it tested broke emissions limits set by EU regulations, according to the consumer organisation.

This is despite all of the vehicles tested by the consumer organisation complying with the same legal limits when using current EU regulatory New European Drive Cycle (NEDC) emissions testing, which takes place in laboratories rather than by driving the vehicles on the road.

Which? said that it carried out the study inside its own independent laboratories using a ‘rolling road’ much like the official EU testing regime, with no testing of cars actually taking place on the road.

And, the consumer organisation argues that in addition to making its results more comparable with official testing, the Which? test cycle is also “more representative of how we really drive on the roads”.


In light of revelations surrounding the Volkswagen emissions scandal, Which? extracted and analysed detailed emissions data for more than 300 cars tested by the consumer organisation since 2012.

The study results published today also claim to show that one in 10 petrol cars also emitted more than the EU nitrogen oxide (NOx) limits allow.

Meanwhile, two-thirds (65%) of petrol cars were also unable to meet the 2006 legal limit for carbon monoxide (CO) under real world driving conditions, with one model producing five times the limit in the Which? test, the organisation said.

And, it also noted that as many as 38 of the cars tested in real-world driving conditions by Which? were unable to meet emissions standards from more than two decades ago in 1993.

Hybrid vehicles were also tested, with results showing that both petrol and diesel hybrids produced more NOx and CO in the real world than current laboratory-based testing limits allow.

New test proposals

New testing methods designed to better reflect real-world driving in order to give a more accurate assessment of vehicle emissions are currently being discussed at EU level, with a view to being introduced from 2017.

However, these current proposals for a new testing regime have faced criticism from MEPs and campaigners for not being strict enough, and for not being brought in sooner.

Which? has also called for the proposals to be brought in “without delay”, and for the government to “set out how it is working with the European Commission and other member states to implement these tests as soon as possible”.

Executive director of Which? Richard Lloyd said: “Car emissions and fuel claims are important factors when buying a new car, so drivers will be shocked by the results of our testing. The current official tests are clearly not fit-for-purpose and we urgently need a new regime putting in place that reflects the reality of how we drive.”

Which? has urged the government to act on the following points:

  • to set out how it will work with the European Commission to implement new tests for car emissions and fuel economy before 2017
  • To set out a timetable for its testing, outlining when UK consumers can expect preliminary and final findings and conclusions.
  • To demonstrate how this investigation will be genuinely independent, including the role of the Vehicle Certification Agency and the contribution of manufacturers (including randomised car testing)
  • To clarify whether the testing regime for Volkswagen vehicle emissions has been manipulated or loopholes exploited specifically in the UK and whether this extends to both fuel efficiency tests and all car manufacturers.


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