The highest court in the home of Volkswagen and BMW has reached a verdict: And it goes against some diesel cars.

The Federal Administrative Court in Leipzig ruled that cities have the right to ban some heavily polluting diesel cars. The decision could drive manufacturers away from combustion engines and force them to improve exhaust systems.

The decision comes as Germany works on how to improve its air quality. The EU introduced limits on levels of particulate matter and nitrogen dioxide in 2010, and many German cities exceed them – including Stuttgart, which has recorded particulate levels over twice the limit. The country has considered measures such as free public transit in its cities to decrease the use of cars.

NPR's Soraya Sarhaddi Nelson reports that proposed bans could affect more than 12 million vehicle owners. But she also notes that Stuttgart's mayor says he has a shortage of police officers to enforce a ban.

The court's decision comes after Environmental Action Germany sued officials in Stuttgart and Düsseldorf to force them to impose bans to stay within EU pollution limits. Now, these diesel bans in Stuttgart and Düsseldorf can proceed with some modifications, according to the Washington Post.

The ruling also sets a precedent for similar bans in other German cities, as long as officials cannot find other ways to reduce nitrogen oxide emissions to EU approved levels. "Of the 15 million diesel cars on Germany's roads, only 2.7 million have Euro-6 technology," reports Reuters. Euro-6 is the latest EU-designated emission requirement cars must meet to reduce harmful pollutants from exhausts. The wire service added,

"Cars that meet Euro-4 emissions standards could be banned from Stuttgart from next January, while Euro-5 vehicles should not be banned until Sept. 1, 2019, four years after the introduction of the latest Euro-6 standard. Tradesmen and some residents should be exempted, the court added. Environment Minister Barbara Hendricks said bans could still be avoided if automakers agree to pay to upgrade the exhaust cleaning systems of older diesels. ... The government has begun work on legal changes to permit driving bans on certain routes on an emergency basis."

Environmental groups celebrated the court's ruling. Tuesday was "a great day for clean air in Germany," head of Environmental Action Germany Juergen Resch told Reuters.

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