UBC Theses and Dissertations
Modeling and mitigating the climate and health impacts of emissions from public transportation bus fleets : an integrated approach to sustainable public transportation Gouge, Brian D.
Public transportation has been widely promoted as a means of increasing the sustainability of urban transportation systems; however these systems also have adverse impacts. Further, although transit agencies are making efforts to address these impacts, the assessment tools and mitigation options available to them are limited. An integrated assessment model was developed to explicitly address the adverse climate and health impacts of the primary exhaust emissions from heavy-duty transit bus fleets. Models of the climate and health impact pathways were developed at several different spatial scales (e.g., macro, meso, and micro). These models were used to quantify the potential of a novel operational control strategy based on vehicle scheduling optimisation to reduce the impacts and costs of operating transit bus fleets. In addition to demonstrating the benefits of the vehicle scheduling optimisation, the results showed that transit agencies that optimise for operating costs and/or climate impacts alone may inadvertently increase health impacts and highlight the need for an integrated assessment approach. In developing the health impact pathway model, particular attention was devoted to evaluating methods of modeling vehicle activity and emissions and the implications of these methods on estimating exposure and health impacts. In comparison to micro and meso scale assessments, traditional regional/macro scale assessments based on emissions inventories were found to underestimate exposure and health impacts because they do not account for the intra-regional spatial variability in, and relationship between emissions and populations. Further, traditional distance-based emission factor modeling approaches were found to poorly characterise the spatial distribution of emissions as well as underestimate total emissions in comparison to modal modeling approaches because they do not fully account for the effects of vehicle activity. However, while modal modeling approaches likely have several advantages over emission factor modeling approaches, an evaluation of a major new modal emissions model developed by the United States Environmental Protection Agency, MOVES, revealed significant biases in the model’s predictions of NOX, PM, and THC emissions from both diesel and CNG transit buses. This suggests that with respect to transit buses, MOVES would benefit from further calibration and its predictions should be interpreted with care.
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