The south-western German city of Stuttgart has called on residents to leave their cars at home indefinitely to reduce harmful air pollution levels that have fallen foul of EU standards for years.
Stuttgart imposed the voluntary ban from midnight on Monday after repeatedly recording fine particulate matter levels that exceeded the 50-microgramme-per-cubic-litre limit imposed by the European Union.
Often referred to as "car city" because Daimler and Porsche are headquartered there, Stuttgart is the most polluted city in Germany. Its location in a basin means that harmful particulate matter gathers there due to a lack of rainfall, low wind speed and other factors.
Residents are being encouraged to use public transport and take part in car-sharing initiatives. The current ban is voluntary, but city officials have said that there may be a fine for non-compliance in the future if air pollution is not reduced.
Residents of Stuttgart and environmentalists have protested at the measure, arguing that the city should impose a legally binding ban on diesel-engine cars instead of asking the city's 200,000 commuters to leave their cars at home.
Fine dust particles are harmful to health and can cause cancer in the long term. It is unclear how long the car ban will last but the German Weather Service says it may be a week before air pollution can be reduced.