Chengdu has partially two levels of BRT. And the main layer is at the height of a 6th/7th floor. 2 winters ago I couldn't see the ground from the bus window bec

Chengdu has partially two levels of BRT. And the main layer is at the height of a 6th/7th floor. 2 winters ago I couldn't see the ground from the bus window because of air pollution. Apparently 6 floors is enough.