Paris and London are enforcing restrictions on the use of older, polluting cars and are considering tougher rules.

The new rules in Paris, which took effect on July 1, bar vehicles built before 1997 and motorcycles built before 1999 during weekday daylight hours. The ban will become progressively more restrictive until 2020, when only cars registered after 2011 and motorcycles registered after July 2015 will be permitted.

Mayor Anne Hidalgo has been candid about her desire to expand the ban to cut back on smog from diesel cars and to “reclaim” the city for pedestrians and bikers, according to ClimateWire. Paris has been cited as having some of the dirtiest air in Europe outside of

Moscow or Milan, according to data gather by the World Health Organization.

London’s new mayor, Sadiq Khan, has proposed higher taxes on polluting vehicles coming into a downtown “low emissions zone,” like diesel cars or older models.

SEE ALSO: More Cities Consider Tough Measures to Fight Congestion

BMI Research reported that regulations restricting vehicle usage in London and Paris could alter the patterns of demand for new vehicle sales of different fuel types if they become models for other cities to follow.

“Given the political influence of both Paris and London, these policies could represent the bellwethers for broader anti-pollution legislation that will emerge across other cities in the UK and France or even Western Europe,” BMI said.

Oslo, Norway, will ban cars from its downtown entirely by 2019. Other cities in Europe and Asia have implemented various partial bans or fees to cut down on private vehicle use and air pollution.

The Detroit Bureau