Spatiotemporal lifecycle assessment of the light-duty vehicle fleet of United States

Abstract

Greenhouse gas (GHG) emission generated by vehicular transportation is one of the most significant challenges facing the world. Automotive manufacturers are actively pursuing technological solutions, such as electrification and light-weighting, to mitigate the emission burdens. However, it remains challenging to understand the actual emission payoff of these technologies, since the real-world driving context and characteristics vary greatly. The recent rapid growth of a new mobility behavior, ride-hailing, has also raised important questions for urban transportation and sustainability, largely because the net environmental impact of ride-hailing services is similarly challenging to assess. In this dissertation, I develop techniques aimed at treating these complex, context-dependent assessment challenges and address two questions: 1) What is the cost optimal technology portfolio required to achieve the environmental targets for the light-duty vehicle fleets? 2) How do the emerging ride-hailing services influence the carbon footprints of light-duty vehicles? This thesis presents my work on the first regionally explicit (county-level) lifecycle assessment of two technologies directed at mitigating the GHG emissions of light-duty vehicles in the U.S. - lightweighting and electrification. Regional differences in climate, electric grid mix, and driving patterns compound to produce a significant regional heterogeneity in the GHG benefits of electrification. We show that lightweighting further accentuates these regional differences. I then expand the scope to incorporate the dynamic evolution of the light-duty vehicle fleets. Through evaluating the lifecycle emission and ownership cost, I identify the most cost-effective technology portfolios of the county-level vehicle fleets that meet specified environmental targets (as the fleet evolves over time/over the course of fleet evolution?). Finally, to tackle the second question of changing modes of vehicle use, I developed the first elaborate, systematic and data-centric study on the environmental sustainability of ride-hailing in major American cities. Through the use of increasingly available large datasets describing vehicle trips within urban areas, I demonstrated that, while ride-sharing leads to positive environmental impacts, the rebound arising from shifts away from mass transit toward ride-hailing engenders substantial negative impact. Results show that the environmental impacts of ride-hailing are strong functions of urban context and vehicle technology, and ride-hailing is unlikely to achieve net environmental benefits without regulatory intervention. These findings fill an important gap in people's understanding of the advanced automotive technologies and the emerging mobility behavior from sustainability perspective, and shed light on the recent upheaval that vehicular transportation has caused across the United States.