In Europe there are discussions about free public transportation to reduce pollution in cities. Even when in Germany first attempts failed due to economical and political arguments, the discussion about it is not yet finished.
Initially I was looking for cities that have introduced "free public transport" to estimate in a second step what impact it might have had on sustainability of the respective ambient (e.g. consumption of area for streets and parking, climate in cities, pollution on fruits from urban gardening, life style in general, mobility, animals in cities, total energy consumption, ability to electrify transport systems, etc.).
In the meantime I discovered lists of cities where "free public transport" was introduced, not knowing whether these lists are complete. Free public transport cities 1 and Free public transportation cities 2. The further link points to some Pros and Cons. But they do not cover all aspects of sustainability, focussing rather more on general political, economical or social aspects Free public transport.
Hope this question now fits to this community.