The German government is considering plans to make public transport free in cities suffering from poor air quality.

The idea was set out in a letter, sent to EU Environment Commissioner Karmenu Vella, and was signed by German Environment Minister Barbara Hendricks, Agriculture Minister Christian Schmidt and chancellery chief Peter Altmaier.

Germany has been under pressure from the European Commission, which in January promised to get tough on air quality and threatened to penalise members that breached EU rules on pollutants such as nitrogen oxide and particulate matter.

German authorities face legal action because of air quality problems in cities.

In the letter, the authors proposed low emission zones, free public transport to reduce car use, extra incentives for electric cars and technical retrofitting for existing vehicles as long as this is effective and economically feasible.