Environmental Justice Concentration Zones for Assessing Transportation Project Impacts

Abstract

Environmental justice (EJ) becomes a concern when minority or low-income communities (referred to as EJ populations) are disproportionately affected by transportation projects. The disproportionate impacts may relate to social, economic, or environmental burdens that EJ populations living in affected project areas will be forced to endure. An important component of any EJ assessment methodology is therefore the identification of EJ communities in a project area. The conventional approach classifies communities by means of threshold values into target and nontarget EJ populations. Research has demonstrated, however, that threshold values are largely influenced by the chosen community of comparison. In addition, the spatial distribution of target and nontarget EJ populations within the affected area changed when the scale of geographic analysis changed. Because it has been argued that effective EJ analysis should consider all minority and low-income population groups regardless of their size, this research presents an innovative approach to identify the concentration of EJ individuals in affected project areas. The approach consists of five steps. First, the spatial distribution of minority and low-income populations is estimated by means of census data at the block level. Second, local measures of spatial autocorrelation for EJ populations are computed for each census block. Third, the EJ concentration levels are conceptualized on the basis of spatial-cluster patterns. Fourth, the concentration levels of minority and low-income populations are combined into a single raster model. The outcome is a map in which each cell has a value that represents its concentration level. Finally, these values and specified spatial connectivity criteria are used to define EJ concentration zones. The objective of this paper is to describe the approach and to present the results from testing it.