Mercedes-Benz, Honda, Mazda and Mitsubishi have joined the growing list of manufacturers whose diesel cars are known to emit significantly more pollution on the road than in regulatory tests, according to data obtained by the Guardian.
 
In more realistic on-road tests, some Honda models emitted six times the regulatory limit of NOx pollution while some unnamed 4×4 models had 20 times the NOx limit coming out of their exhaust pipes.

“The issue is a systemic one” across the industry, said Nick Molden, whose company Emissions Analytics tested the cars. The Guardian revealed last week that diesel cars from Renault, Nissan, Hyundai, Citroen, Fiat, Volvo and Jeep all pumped out significantly more NOx in more realistic driving conditions. NOx pollution is at illegal levels in many parts of the UK and is believed to have caused many thousands of premature deaths and billions of pounds in health costs.

All the diesel cars passed the EU’s official lab-based regulatory test (called NEDC), but the test has failed to cut air pollution as governments intended because carmakers designed vehicles that perform better in the lab than on the road. There is no evidence of illegal activity, such as the “defeat devices” used by Volkswagen.