Effects of Scale and Boundary Selection in Assessing Equity of Transit Supply Distribution

Abstract

The equitable distribution of transit services is a major concern of transportation planners and policy makers worldwide. In the United States, planners are required by executive order to consider equity concerns when investing in new transportation infrastructure and services. However, equity can be difficult to assess in a consistent, objective, and quantitative way. Australian researchers recently developed a single, systemwide measure that reflects the equity of transit service distribution in a metropolitan area. This measure, known as a Gini coefficient, measures specifically how well transit supply meets transit demand. Transit supply is measured with a modified form of an established supply index, and demand is estimated with population and employment data. Although the idea of a single measure for assessing the equity of a transit system is appealing, researchers and practitioners must be careful when they implement Gini coefficients for comparative purposes. This research investigated the effect of selecting various scales, boundaries, and demand measures for calculating Gini scores for interregional comparisons. Gini coefficients were calculated for six urban transit systems within two boundaries (metropolitan statistical area and transit service area) at two scales (census tract and block group) with two demand measures (population and population plus employment). Results suggest that calculations with Gini coefficients on the basis of various boundary definitions can lead to drastically different comparative results, whereas the different scales and demand measures had little impact on interregional comparisons.

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