After a top court last month ruled driving bans in some city zones for the most polluting diesel vehicles were legal, German commuters, politicians, environmentalists and the mighty car industry have been exchanging blows over potential blanket exclusions.

Instead, “city toll systems can be an effective tool to clean up the air in cities” and help avoid “very frustrating” outright bans, Bulc told the Mitteldeutsche Zeitung newspaper.

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An electronic levy system — possibly standardized across the European Union — could allow national governments to introduce “dynamic tariffs, for example depending on levels of harmful emissions or the time of day,” Bulc added.

Costs to set up systems to track cars entering toll zones and charge their drivers would be high, the commissioner acknowledged, “but would pay off quite quickly both from a financial perspective and in terms of the environment and protecting health” of city dwellers.

Bulc added that she was “not sure whether free public transport” was necessary to fight air pollution.

The controversial suggestion was made by the German government in a letter to Brussels last month, as one of a range of possible measures Berlin is pondering to reduce pollution and avoid fines over smog-choked air.

“It's more important to make public transport available for as many people as possible in the first place,” Bulc said.

British capital London last year introduced a “Toxic Charge” of 10 pounds (€11.18 or $13.87) per day on the oldest, most polluting vehicles built before 2006, on top of a general 11.50-pound “congestion charge” for vehicles entering the centre.

Britain and Germany are among nine EU countries to overshoot a Brussels-imposed deadline to clean up polluted air, which is blamed for around 400,000 premature deaths each year in the EU.