​Summary: This study examines whether the “Emission Reduction Plan for Ports and Goods Movement” in California reduced air pollution exposures and emergency room visits among California Medicaid enrollees with asthma and/or chronic obstructive pulmonary disease.

Authors created a retrospective cohort of 5,608 Medicaid enrollees from ten counties in California with data from 2004 to 2010. They grouped the patients into two groups: those living within 500 meters of goods movement corridors (ports and truck-permitted freeways), and control areas (away from the busy truck or car permitted highways). Authors created annual air pollution surfaces for nitrogen dioxide and assigned them to enrollees’ home addresses. They used a quasi-experimental design with a difference-in-differences method to examine changes before and after the policy for cohort beneficiaries in the two groups.

Findings: The reductions in nitrogen dioxide exposures and emergency room visits were greater for enrollees in goods movement corridors than those in control areas in post-policy years. Researchers found that the goods movement actions were associated with 14.8% greater reduction in emergency room visits for the beneficiaries with asthma and chronic obstructive pulmonary disease, respectively, in the third year after California's emission reduction plan.

These findings indicate remarkable health benefits via reduced emergency room visits from the significantly improved air quality due to public policy interventions for disadvantaged and susceptible populations.