Where to Draw The Line: Impacts of Threshold Choice on Measures of Transport Poverty

Distributive concerns in transportation equity can be evaluated either in terms of inequality (e.g., how equal are distributions?) or sufficiency (e.g., how many and what kinds of people lack access to the transportation resources they need?). Sufficiency analyses offer more actionable insights that can be used to mitigate transportation disadvantage, but related analytical methods 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, (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 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, that population-weighted percentile measures may allow for better comparisons across demographic groups, and that by most reasonable definitions of transport poverty the vast majority of residents (80+%) in an area might be considered to be in transport disadvantage.