Petrol and diesel cars will not be allowed within the zones in the effort to improve air quality across the city. Such a scheme is the first of its kind however it is hoped that this will be a highly significant introduction which will encourage other global cities to follow.
Read further, and the response of the Mayor of Paris, Milan and Copenhagen here: https://airqualitynews.com/cars-freight-transport/stockholm-to-ban-petrol-and-diesel-cars-from-start-of-next-year/