London will close 20 kilometres of road as part of a car free day to tackle air pollution in September , the city’s mayor Sadiq Khan has announced. Eighteen of London’s 32 boroughs have signed up to the event, which will close the city’s iconic Tower Bridge and much of its financial centre on September 22. The Mayor is asking Londoners to "reimagine" a city where public transport is king instead of the car. Currently 63 per cent of journeys in the city are made by sustainable transport - a figure Mr Khan wants to increase to 80 per cent by 2041. Some of the closed roads will host ‘Play Streets’ where community activities will take place, and Londoners and visitors alike will be able to cycle and walk in areas usually closed to the public. “I encourage as many Londoners as possible to join in the fun and see the city from a different perspective,” Mr Khan said. “I will continue to work with those boroughs who are forward-looking and want to think differently about how to use road space. Hopefully this will shame into life those boroughs with outdated views who are dragging their feet”. More than 50 per cent of London’s toxic air pollution is caused by vehicles, but a recent Transport for London survey found that almost one in two Londoners did not realise vehicles were the main cause of air pollution, although three in four Londoners were worried about the health impact. Campaigner Jemima Hartshorn, founder of Mums for Lungs, welcomed the news, adding she hoped the day would show how “healthy, fun and accessible” London is without the need for road transport. “We are pleased the Mayor is supporting Car Free Day in London so strongly. Air pollution is killing thousands of Londoners prematurely every year and making many more people sick,” she said. Dr Audrey de Nazelle, Senior Lecturer at the Centre for Environmental Policy at Imperial College London, said the scheme is a “wonderful way to engage citizens”. “Being aware of the scale of air pollution health problems is not enough, actually living the joys of a car-free or car-less city will do much more to create a positive vision of what a future healthy London could be like,” she said. The announcement of London’s car free day follows Scotland's capital Edinburgh announcing it will close its city centre streets to cars for the first Sunday of every month to tackle air pollution.