Bumper to Bumper: Do intra-urban disparities in traffic density represent an “intervenable” measure for reducing intra-urban disparities in air pollution?
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Objective: Evidence suggests that historical redlining, the institutionalized practice of discriminatory mortgage lending, in the United States is associated with present-day inequalities in environmental exposures, including air pollution. While neighborhood-level disparities in traffic-related air pollutant concentrations have been observed, the role of traffic density has not been well-characterized. We examine associations between traffic density and Home Owners’ Loan Corporation (HOLC) neighborhood grade (i.e., historical redlining) across five cities in North Carolina.
Materials and Methods: Average annual traffic density (vehicle miles traveled (VMT) per square mile) for all primary and secondary roads were calculated for each North Carolina census block group for 2015. Using these data, the weighted average annual traffic density was calculated for each of 123 HOLC polygons with grades ranging from “best” to “hazardous” (A – D). Linear regression models were fit to estimate unadjusted associations between traffic density and HOLC grade.
Results: In 2015, the median traffic density across all HOLC neighborhoods was 63,817 VMT per square mile (interquartile range: 36,329 to 111,718; mean: 85,707). On average, less desirable HOLC grades were consistently associated with higher average traffic density values; each increase in HOLC grade (from A towards D) was associated with a ~26% increase in traffic density (p = 0.01). A pronounced difference was observed between grade A and grade D neighborhoods; redlined neighborhoods (grade D) had 78% higher average traffic density compared to grade A.
Conclusions: Differences in traffic density by HOLC grade may account for some current-day air pollution disparities observed across historically redlined neighborhoods. Traffic density may play a role in the ongoing disproportionate burden of environmental exposures related to historical redlining. Targeted efforts to reduce traffic density in historically redlined neighborhoods may reduce inequities in traffic-related air pollution exposures and their associated health effects.