The cost of not having free public transit

We have tried to list all the externalities of the private auto and sprawl. But the list keeps growing and growing. People ask, "can we afford to have free public transit"? The answer is "we can no longer afford not to have it". In the article quoted below fromClimateProgress they show how NRC counts more externalized costs.

...The report estimates dollar values for several major components of these costs. The damages the committee was able to quantify were an estimated $120 billion in the U.S. in 2005, a number that reflects primarily health damages from air pollution associated with electricity generation and motor vehicle transportation. The figure does not include damages from climate change, harm to ecosystems, effects of some air pollutants such as mercury, and risks to national security, which the report examines but does not monetize... NationalResearchCouncil via ClimateProgress