The Line Must Be Drawn Here: Impacts of Parameter Choice on Access Disadvantage Measures

Transportation equity researchers typically quantify either inequality (e.g., how equal are distributions between groups?) or sufficiency (e.g., how many and what kinds of people lack adequate access to the transportation resources?). Sufficiency analyses offer more actionable insights that can be used to mitigate disadvantage, but fundamental analytical methods for sufficiency analyses are not well developed. To advance this area of research and practice, this paper investigates three approaches to measuring sufficiency through the lens of public transport access to jobs: (i) fraction of total regional destinations reachable, (ii) competitiveness with auto access, and (iii) population-weighted percentile measures. We use a class of decomposable Foster-Greer-Thorbecke poverty measures to understand the sensitivity of overall levels of disadvantage to the choice of disadvantage lines (sufficiency thresholds) and other parameters, in the context of seven U.S. urban regions. We find that fractional and auto competitiveness measures produce similar results and are highly sensitive to the choice of disadvantage line, population-weighted percentile measures may allow for better comparisons across demographic groups, and by most reasonable definitions the vast majority of residents (80+%) in an area might be considered to experience access disadvantage.