A modern diesel car pumps out more toxic pollution than a bus or heavy truck, according to new data, a situation described as a “disgrace” by one MEP.

The revelation shows that effective technology to cut nitrogen oxides (NOx) pollution exists, but that car manufacturers are not implementing it in realistic driving conditions.

Diesel cars tested in Norway produced quadruple the NOx emissions of large buses and lorries in city driving conditions, according to a report from the Norwegian Centre for Transport Research. A separate study for Transport for London showed that a small car in the “supermini” class emitted several times more NOx than most HGVs and the same amount as a 40-tonne vehicle.

“It is crackers,” said emissions expert James Tate from the University of Leeds. His own research, which uses roadside equipment to measure passing traffic, also shows the latest diesel models cars produce at least as much NOx as far heavier buses and trucks.

The issue of NOx pollution, thought to kill 23,500 people a year in the UK alone, gained prominence when VW diesels were discovered to be cheating official US emissions tests. The scandal also led to revelations that the diesels of many car manufacturers produce far more NOx on the road than in EU lab tests, though not via illegal means.

The UK government say the failure to keep NOx from vehicles low in the real world means road transport is “by far the largest contributor” to the illegal levels of NOx in many parts of the country.

“It is disgraceful that car manufacturers have failed to reduce deadly emissions when the technology to do so is affordable and readily available,” said Catherine Bearder, a Liberal Democrat MEP and a lead negotiator in the European parliament on the EU’s new air quality law.

“The dramatic reduction in NOx emissions from heavier vehicles is a result of far stricter EU tests, in place since 2011, that reflect real-world driving conditions. If buses and trucks can comply with these limits, there’s no reason cars can’t as well.”

Greg Archer of Transport & Environment said: “Carmakers claims [that] new diesel cars are clean are preposterous. Governments must ignore the bleating of carmakers for lenient limits and fix the problem for good.”



Both the Norwegian and London research tested vehicles meeting the newest and strictest Euro6 standard in similar lab-based tests that – unlike EU official regulatory tests – are realistic simulations of city driving.

At the Norway Centre for Transport Research, the researchers found “all [12 of] the tested heavy vehicles’ engines have very low emissions of NOx in real traffic” and that emissions had fallen tenfold from the previous models. But the seven diesel cars emitted four times more on average than the trucks and buses.

The Norwegian team concluded: “Test results have shown by effective removal of NOx from the exhaust gases of heavy vehicles that it is possible with Euro 6 engines. This means that it is technically possible to achieve the same positive results for new generations of cars with diesel engines.” They also found that in cold weather the NOx from diesel cars soared to 11 time official levels.

The Transport for London research compared nine diesel cars, ranging from the super-mini class up to SUV, against three HGVs and one LGV. The NOx emitted from the cars was similar to that from the heavier trucks though one car – the smallest diesel tested – produced more than double the 12-tonne lorry and the same as the 40-tonne vehicle.

Tate said the reasons car manufacturers were not implementing the NOx reduction technology on cars were convenience and cost. The most common technology requires a chemical compound known as urea to be squirted into the exhaust gases, but a large urea tank would be heavy while a small one would require frequent refills. “It’s not really the image the manufacturers are looking for: you are in your smart suit filling up your expensive car – with urea,” he said.

In contrast, truck and bus drivers are happy to refill the urea tanks and the additional cost of the technology is easier for buyers of large and expensive vehicles to bear.