Warsaw Municipality in Poland built mini gardens on the roof of the bus stops in order to reduce air pollution and green the city. The first garden was built on the roof of a bus stop in Zoliborz district last year. Authorities determined to build such gardens on other bus stops as the sedum plant was resistant to high temperatures in summer, and snow and frost in winter. It is aimed that the application, which currently covers 18 bus stops, will spread to the whole city in near future.