Multiple lines of evidence suggest that our core qualitative results align with available observational evidence. A relative strength of our modeling approach is that it allows us to model temporal changes at sufficiently high spatial resolution that we can estimate exposure disparities attributable to individual source categories. In contrast, a detailed longitudinal record of in-situ observations is not available at sufficient spatial resolution to permit rigorous assessment of how disparities in exposure to traffic-related PM2.5 have evolved. Nonetheless, CARB's analyses of ambient monitoring data from 1990-2014 align qualitatively with our results. These analyses of monitoring data indicate declining concentrations of diesel PM, PM2.5, and NO2, but with persistent relative and absolute disparities for the relatively sparse network of sites located in overburdened communities .