A worker removes a marker to validate a sign that bans access for older-model diesel cars on a street on May 30, 2018 in Hamburg, Germany. The city is launching the project on two stretches of busy streets in the city center in an effort to improve air quality there. A number of German cities are facing litigation by the European Commission over failing to meet E.U. air quality standards. Banning older model diesel cars is a measure many city authorities are discussing but that remains controversial.