A comparative analysis of the challenges in measuring transit equity: definitions, interpretations, and limitations

In the study of equity in public transit service distribution to disadvantaged groups, there is often a desire for a concise and relatable quantitative measure of equity. This ambition has often pushed researchers to develop methods for combining (or aggregating) various dimensions of disadvantage into a single, multi-faceted metric of potential transit demand (or need) among the disadvantaged population. These metrics then enable a somewhat straightforward analysis of the transit needs of the aggregate disadvantaged population to the transit service supplied in order to arrive at a measure of transit equity. More recently, it has been proposed that such aggregated transit equity analysis may introduce veiled judgments or bias through the specific interpretation of key definitions and through the particular choices in the construction of a combined metric. It may also be the case that such an aggregate metric may mask or convolute important disparities in transit equity experienced by the various disadvantaged populations aggregated into a combined metric. This research studies these issues through a clear discussion of the ambiguity and implied judgments often found in transit equity literature and then provides recommendations to mitigate these issues. Also, two common equity analysis methods are compared through a case study of public transit service in the city of Corvallis, Oregon, and a new transit service metric construction is introduced. By comparing the results of both the aggregated and disaggregated forms of disadvantaged group transit need within each analysis method, this study provides further evidence that important information may be concealed or easily misinterpreted when using aggregated descriptions of transit need.