Near Roadway Air Quality
Interest in the roadside environment has been steadily increasing since the late 1970s, driven by possible links between poor air quality near heavily traveled roads and health outcomes in exposed individuals. Substantial generators of local traffic, such as marine terminals can bring the additional problems of noise and decreased pedestrian safety and accessibility to streets lined with schools and homes. This thesis has two aims: to synthesize the knowledge on observed air pollution concentrations near roadways, and to assess the air quality effects of a local diesel truck traffic mitigation project while providing an overview of its planning. Each is addressed in its own part. The first presents the results of a meta-analysis of observed near roadway air pollution concentrations. In total, 34 studies were identified from which 572 pollutant concentrations and their associated distances from the road were extracted. Normalization was necessary to increase data commensurability. Using the edge of road concentration to normalize grouped observations more closely than using the background concentration, but the results of two statistical analyses (local regression and analysis of variance) performed on both datasets showed broadly consistent results: carbon monoxide, elemental carbon and surrogates, metal deposition, oxides of nitrogen, non-alkane hydrocarbons, and ultrafine particle number are consistently elevated, reaching between 1.7-20 times above background at the edge of road, depending on pollutant and normalization method. Most pollutants decay to background by 150 m from the edge of road. The second part examined a series of measures to mitigate local diesel truck impacts at two port facilities while improving traffic operations in the communities of Barrio Logan, San Diego and Old Town, National City, both low-income communities of color. This subject moved the thesis beyond an exclusive focus on air quality and provided the first documentation of the unique process and solutions which emerged following the collaboration of all major stakeholders. Local truck impacts and heavily mixed land uses provided the impetus for the mitigation which resulted in a permanent rerouting of all trucks over five tons to roads outside of the communities. Previous assessments of the project described the extent to which mitigation strategies are expected to improve traffic operations or claimed air quality improvements without carrying out an emissions analysis. We performed a local-scale analysis of the effects of traffic volume and speed changes on diesel particulate matter (DPM) emissions in Barrio Logan. We find that, while the mitigation did not result in improved regional air quality, it did significantly improve local air quality in the primary affected corridor, resulting in a 99 percent reduction in DPM emissions, and an 87 percent reduction in diesel truck vehicle miles traveled.