The new initiatives will award each car model a score based on all of the air pollutants they release during real-world, on-road conditions. The scores will be made easily available to citizens through dedicated websites. Consumers will therefore enjoy a far more accurate understanding of how polluting that car will be when driven on urban streets. Paris and London have committed to launch their data online by the end of 2017.

Several other C40 cities, including Seoul, Madrid, Mexico City, Milan, Moscow, Oslo and Tokyo have committed to work with C40 to develop a global scoring system relevant and accessible to all citizens, and will explore how to provide this accurate and transparent information to the public.

The existing EU labeling scheme only rates vehicles for fuel efficiency and CO₂ emissions, and are based on laboratory tests. Research has shown that current testing schemes conceal the real-world levels of toxic emissions. Some diesel cars that meet the latest Euro 6 standards in reality release more NO_x than a modern heavy duty truck. (Earlier post.)

Zurich remote sensing data shows a wide disparity between petrol and diesel car NOx emissions, and substantial noncompliance by diesel cars. Source: The ICCT. Click to enlarge.

Although the upcoming Real Driving Emissions (RDE) regulation will address the issue of excessive NO_x emissions, phase in will be slow and effectiveness limited, the ICCT observed. The RDE will only be fully in place by January 2021, and in its likely final version, real world NO_x emissions are still expected to be more than twice the regulatory limit, and three times higher than for gasoline vehicles, the ICCT said.

Other labeling schemes, such as the Crit’Air program, certify vehicles’ environmental class based on pollutant emissions, and may distinguish diesel from gasoline powertrains. The City of Paris uses the Crit’Air program to incentivize the cleanest vehicles and ban older vehicles that emit more air pollutants.

Independent real-world emissions testing by the ICCT and others confirms the effectiveness of this approach for certain pollutants, which are emitted in greater quantity by older vehicles: hydrocarbons, which are ozone precursors; carbon monoxide; and fine particles, which are important causes cardiopulmonary disease.

However, the ICCT notes, labeling by itself in insufficient to address the problem of diesel vehicles. On average, European passenger diesel cars emit NO_x emissions under real world driving conditions that are seven times the regulatory limit. (Earlier post.)

Even vehicles that meet the latest (Euro 6) emission standard in most cases (but not all) emit excessive amounts of NO_x in real-world operation. Real world testing data from testing campaigns in German, the UK, France, and other Member States shows that the majority of Euro 6 vehicles are still emitting NO_x at several times legal limits.

The mayoral announcement was made following a closed-door meeting between mayors, senior city officials and representatives of several major car manufacturers, designed to find ways to accelerate the transition to low-emission and electric cars. The meeting, was the first such effort by city leaders and car manufacturers to work together in planning for a sustainable future.