Study of Freeway Capacity Increases in the San Francisco Bay Area and Greater Sacramento

摘要

The study evaluates the adequacy of freeway capacity increases' air quality analyses and the accuracy of their predictions of future traffic volumes. New alignment freeways, freeway lane additions, and freeway interchange additions or expansions in the greater Sacramento and greater San Francisco Bay Areas, planned in the last 10 years, were all included in the study. The California Environmental Quality Act (CEQA) and/or National Environmental Policy Act (NEPA) documents for these projects gave the needed air quality analyses and traffic predictions. The study revealed simplistic air quality analyses. Only 22% of the projects analyzed meoscale emissions of CO, NOx, and hydrocarbons; the rest of the projects had only microscale analysis of CO emissions or no quantitative emissions analysis whatsoever. Despite shortage of detailed traffic count data in the Bay Area, the study showed a pattern of traffic projections that significantly underpredicted the observed actual volumes. Thus, these freeway capacity increases appear not to have had the predicted regional air quality benefits, but instead have likely worsened air quality.