The Düsseldorf Administrative Court had directed the State of North Rhine-Westphalia, following a complaint by the environmental organization Deutsche Umwelthilfe, to amend the Clean Air Plan for Dusseldorf so that it could take the necessary measures to ensure that the NO₂ limit value of 40 μg/m³ averaged over one year is met as soon as possible contains in the city of Düsseldorf.

The state was directed to consider further measures to limit the emissions of diesel vehicles by amending the Clean Air Plan. The Bundesverwaltungsgericht ruled that limited driving restrictions for certain diesel vehicles are legal and not excluded.

The Stuttgart Administrative Court undertook to match the Stuttgart clean air plan to that of the state of Baden-Wuerttemberg in taking the necessary measures for the fastest possible compliance averaged over a calendar year immission limit for NO₂ levels of 40 μg/m³ and the hourly limit value of 200 μg/m³ with a maximum of 18 authorized exceedances in the calendar year in the Stuttgart environmental zone.

The Bundesverwaltungsgericht ruled that the administrative court judgments were largely unobjectionable in the light of EU law. Both EU law and German federal law require, through the use of appropriate measures contained in clean air plans, to keep the period of emissions exceeding the limit values in place since 1 January 2010 as short as possible.

The Bundesverwaltungsgericht noted that contrary to the assumptions of the administrative courts, German federal law does not permit zone-related or distance-related traffic bans specifically for diesel vehicles. According to the federal ordinance on the marking of motor vehicles with a low contribution to pollution (sticker regulation), the enactment of traffic prohibitions based on the emission behavior of motor vehicles is only possible according to their specifications (red, yellow and green sticker).

However, the high court ruled, in the light of the EU law obligation to comply with the NO₂ limit as soon as possible, it follows from the case-law of the Court of Justice of the European Union that national law must be disapplied if this is necessary for the full effectiveness of EU law is.

Therefore, the sticker regulation and the StVO (road traffic regulations, Straßenverkehrsordnung) remain inapplicable insofar as they preclude the obligation to comply with the limit if a traffic ban for diesel vehicles proves to be the only suitable measure to keep the period of non-compliance with the NO₂ limit values as short as possible, the high court said.

With regard to the Stuttgart Clean Air Plan, the Administrative Court had stated that only a ban on all motor vehicles with diesel engines below emission class Euro 6 and for all vehicles with gasoline engines below emission class Euro 3 in the Stuttgart environmental zone would constitute a suitable air pollution control measure.

However, the Bundesverwaltungsgericht ruled, when adopting this measure, as with all measures included in an air pollution control plan, it will be necessary to ensure that the principle of proportionality is respected. In that regard, with regard to the Stuttgart environmental zone, a phased introduction of traffic prohibitions, which in a first stage concerns only older vehicles (eg up to the Euro 4 emissions standard), should be considered, the court said.

In any event, in order to establish proportionality, Euro 5 vehicles may not be subject to traffic bans before 1 September 2019 (hence four years after the introduction of the Euro 6 emission standard). In addition, there are exceptions, eg for craftsmen or certain local groups.

With regard to the Düsseldorf Clean Air Plan, the ruled that if traffic prohibitions on diesel motor vehicles are the only appropriate measures to ensure that NO₂ limit values are exceeded as little as possible, these must be considered in compliance with the principle of proportionality.