European national authorities “encouraged” car manufacturers to produce diesel cars that polluted more than EU limits allowed by insufficiently investigating emissions of cars on the road, a French committee concluded in a report published Friday (29 July).

The report said market surveillance of emissions of diesel vehicles, once sold, was “largely insufficient”.

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“The absence or lack of transparency of surveillance testing and control by public authorities on emissions of vehicles offered for sale in the European Union, constitutes incitement to fraud and therefore must be absolutely corrected,” the committee wrote.

The group was set up in October 2015 by French environment minister Segolene Royal after the Volkswagen emissions cheating scandal raised suspicions about other car manufacturers' behaviour.

It included members from the environment ministry, French MPs, research institutes, environmental and consumer groups, but also representatives from industry.

At the committee's request, France's car certification body carried out emissions tests on 86 vehicles. Just like previous exercises carried out by German and UK authorities, it found that many diesel cars were emitting much higher pollutants on the road than in the laboratory.

The committee concluded that car manufacturers were “systematically” using defeat devices, which switched off or turned down the emissions filter system under certain conditions.

These are banned under EU law, but an exception exists: if they are used to protect the engine.

The authors of the report said it seemed that in some cases the exception was used too freely.

They asked carmakers to explain why the emissions filter is sometimes switched off under normal driving conditions, but complained about lack of cooperation from several carmakers.

“At this stage, the committee has not demonstrated the use of illegal defeat devices, but can not rule them out either,” the report noted.

The committee concluded that car manufacturers designed their diesel cars to pass the test, but not to stay under EU pollution limits in the real world.

“The impacts that this approach generates on the emissions of harmful elements and the air quality near roads seem to have been largely ignored” during the design phase, they wrote.

The report also gave an insight into where the cars were certified. The cars that were tested had mostly been certified in western Europe. However, there appeared to be no correlation to certain testing authorities compared to bad performances on the road.

A Citroen C4 Picasso for example emitted 4.1 times the EU limit when driving on the road. It was tested and approved in France.

A BMW 116D emitted 6.2 times above the limit. It was tested for emissions in Ireland and received its final approval to be sold on the market in Germany.

A Ford C-Max (6.1 times above the limit) was tested for emissions in the UK, and approved in Luxembourg.

The report was delayed several times, and the timing of its publication after 10 months of work is conspicuous.

Originally scheduled to be published in June, the report was finally released on a Friday afternoon in the middle of summer, with public attention diverted by the European holiday season.

The UK and Germany, which carried out similar tests and produced similar results, published their reports in April.