Berlin – Germany's diesel drivers and carmakers have their eyes fixed on the Federal Administrative Court in the eastern city of Leipzig, which is expected to rule on whether bans on such cars can be legally enforced by municipalities concerned about air quality. The following are some of the questions the court is considering:

What is the problem?

European Union pollutant limits have for years been breached in many cities, with the main culprit being NOx - the toxic oxides of nitrogen. These gases affect the airways and eyes with resultant heart and lung problems for some people. According to a study by the Office for the Environment, around 6,000 people die prematurely in Germany each year from ailments linked to NOx pollution. Pollution levels have declined slightly, but the limits are still being exceeded in almost 70 cities. Munich, Stuttgart and Cologne are the worst-affected. Transport contributes 60 per cent of NOx, with diesels making up 72.5 per cent of that. German environmentalists have been pressing their case for years, and there is pressure from the European Commission, with a complaint before the European Court of Justice looming.

What is at issue for the court?

The court could rule Tuesday on whether diesel bans are legally acceptable and can be included in regional air quality programmes without federal regulation. But the Leipzig court will not itself impose driving bans. Air quality programmes from Dusseldorf and Stuttgart are the immediate issue. Following legal action brought by Deutsche Umwelthilfe (DUH) environmental group, the regional administrative courts in those cities ordered the municipalities concerned to act to achieve the NOx limits. The Stuttgart court referred to driving bans as the "most effective" measure, adding that health concerns trumped the interests of diesel drivers. The Dusseldorf court ruled that diesel driving bans needed to be "seriously examined."

What are the effects of the court's ruling?

Even if the court is in fact ruling only on two cities, its decision will have significance countrywide, in particular if it rules that driving bans are legal. Any German city where the limits are breached could impose bans on older diesel cars, but nothing is automatic. It would be weeks or even months before cities include bans in their air quality programmes, with each move being individually tailored to certain roads and at certain times.

What are the consequences of driving bans?

There are millions of diesel cars in Germany. Business and municipalities are warning of paralysis, with shops not getting their deliveries and artisans unable to reach their customers. But there could also be exceptions for these, as there would have to be for the police, fire services and medical services. But many commuters would be hit, and the impact on the automotive sector would be huge. Diesel registrations have been declining, and diesel owners are seeing a sharp drop in the value of their cars. The federal government wants to avoid bans, having introduced an expensive "Cleaner Air" programme involving changes in short-range transport and cleaner buses and taxis. Carmakers aim to cut emissions through software updates. But environmentalists are unimpressed, demanding changes to the engines themselves - which manufacturers dismiss as too expensive.

What role will the Euro 6 blue disc play?

If the Leipzig court opens the way for driving bans, there will be a debate not only about reconfiguring diesel engines and emissions software, but also about introducing a blue disc to show which vehicles meet the latest EU emissions standard – the Euro 6. This would facilitate making distinctions between different diesel vehicles, making a blanket ban unnecessary in polluted urban areas. And a blue disc valid countrywide would avoid a patchwork of regulations unintelligible to the average driver. But the federal government has thus far rejected the idea as implying effective dispossession of millions of diesel owners, noting that only relatively few cars meet the latest standard.