A court in the western German city of Mainz is to consider on Wednesday whether a ban on older diesel vehicles in the urban centre must be introduced in order to tackle air pollution.

Mainz is the latest in a string of German cities plagued by poor air quality where a ban is on the cards. Courts have already ordered similar measures in parts of Hamburg, Stuttgart, Aachen, Frankfurt, and Berlin.

The court is hearing the case based on a complaint lodged by the environmental group DUH against Mainz, which has higher concentrations of airborne nitrogen oxide than permitted by environmental standards.

Mainz says it has already driven down the levels of nitrogen oxide, for example by retrofitting bus exhausts and expanding its tram network.