Identifying environmental justice communities for transportation analysis

Environmental justice (EJ) refers to policy and advocacy intended to achieve equitable protection from environmental harms and access to benefits across demographic groups. Research has shown that low-income communities and communities of color are often exposed to greater harms and enjoy fewer benefits from transportation systems than the general population. However, federally-mandated EJ analyses rarely conclude that projects could result in disproportionate impacts to these communities. This paper investigates the methods used to define EJ communities—a key analytical step for which there is little specific guidance—as a potential driver of variation in observed EJ outcomes. Using a case study of transit accessibility in Fresno County, California, the paper contrasts three methods for the identification of EJ communities: (1) a commonly used threshold-based approach that groups geographic areas using demographics, (2) a population-weighted approach that calculates weighted means of performance measures, and (3) community-based identification of EJ areas. The analysis indicates that the first method is appropriate for targeting transportation investments but not for assessing EJ outcomes, while the second two methods are appropriate for assessing EJ outcomes. Importantly, the method used to define EJ communities can substantially affect the analytical outcome, potentially shifting a finding of inequity from null to positive or vice versa. These results have important implications for transportation planning agencies and transportation service providers that conduct EJ and equity analyses, as a finding of inequity may lead to design changes or mitigations.