Greenpeace activists protest with a symbolic Blaue Plakette (blue badge) in front of Hamburg's city hall, where a conference of ministers of transport is held. The environmental activists protest against dangerous diesel exhaust and ask the ministers to act for a so called blue badge to get dirty diesel out of affected city districts. Banners read:"Ban dirty diesel". Greenpeace traffic expert Benjamin Stephan and minister of transport, Alexander Dobrindt.