Carbon-reduction efforts can have a significant impact on public health. The illnesses we can prevent through transportation and other policy changes that reduce combustion emissions—obesity-related, respiratory, and cardiovascular problems—are among the most prevalent and expensive diseases in many developed countries. If we can improve public health in our cities, we can grow our economies and reduce our carbon emissions at the same time. Here in New York City, we estimate that a modest 10% reduction in particulate matter pollution, a by-product of fossil-fuel combustion, would result in 400–500 fewer deaths each year.