London is already the biggest city in the world to have any form of tax that restricts driving in the center—the congestion charge is currently £11.50 ($18.60) per day to travel into central London during the working week. Exemptions from the scheme include lower-emitting vehicles, motor bikes, and electric cars. The city also has a Low Emission Zone, which applies to the whole of Greater London throughout the year, and charges up to £200 a day for heavy-polluting trucks and buses that come into the capital.

Now, with more than 4,000 people dying from air quality-related illnesses in London every year, the city is proposing a new charge to improve air quality:  an Ultra Low Emission Zone. From September 2020, London wants to charge drivers of some of the most polluting cars an extra £12.50 to enter the city center on top of the congestion charge, meaning the commuters in old cars will need to pay £24. With big trucks, the new charge will rise to as much as £100 a day.

And the move is being pioneered by the city’s Conservative mayor, Boris Johnson, who said introducing “the world’s first ultra low emission zone is an essential measure to improve London’s air quality.” The argument for the new zone is, simply, that all the previous steps that London has taken have worked so far.

The congestion charge, the current Low Emission Zone, as well as retro-fitting buses to make them cleaner and setting age limits on taxis—all have dramatically improved London’s air quality. Traffic accidents are down (paywall).  According to Transport for London, carbon-dioxide emissions have fallen dramatically and the only pollutant that is above European Union regulations is nitrogen dioxide—which will be targeted in the new zone.

Giving motorists a six-year notice allows for the natural churn of vehicles. The city doesn’t really want to charge people so much as encourage them to adopt cleaner vehicles in the run-up to the 2020 start date. Transport for London plans to change regulations to make all taxis zero-emission from 2018, and all of London’s famed double-decker buses will be hybrid by 2020. “I understand that people need adequate time to switch to greener vehicles and help is at hand for those who will be hardest hit, but let’s be clear, we need to make these important changes ASAP to continue to improve Londoners’ quality of life,” Johnson said.

Other cities have tried to mimic London’s congestion charge (itself inspired by Singapore’s)—with mixed results. Milan has one. Mayor Mike Bloomberg’s attempt to introduce one in New York was killed in 2008. Sao Paulo, which has some of the worst traffic in the world, has been trying to implement one for years, with the latest date set for 2025; 80% of drivers oppose it (link in Portuguese). But as everyone tries to manage the traffic of their ever-larger urban conurbations, London is already showing how a modern metropolis can use the carrot and the stick to make the city better for everyone.