The Federal Administrative Court ruled in its fundamental judgments of February 27, 20181 (BVerwG I), that Art. 23 para. 1 subpar. 2 RL 2008/50/EC requires a traffic ban for certain diesel vehicles within an environmental zone or for certain roads or road sections if this is the only suitable measure for the fastest possible compliance with the nitrogen dioxide limit values specified by the directive. The order must comply with the principle of proportionality. These judgments prompted the legislature to insert Section 47 para 4a Federal Emission Control Act (BlmSchG).2 Since then, various decisions by the higher administrative courts/administrative courts have been issued with different statements.3 In the judgment of February 28, 2020 (in the version BVerwG II)4 on the Reutlingen Air Pollution Control Plan, the Federal Administrative Court had the opportunity to further develop and substantiate its case law and to clarify divergences in the case law of the higher administrative courts/administrative courts. The article tries to draw up an interim balance.