Research Team: Scott Samuelsen (lead), Analy Castillo Munoz, and Brian Tarroja
UC Campus(es): UC Irvine
Problem Statement: Many municipalities and state governments have set targets for one or more of the following objectives: greenhouse gas reduction, compliance with air quality standards, and increasing renewable utilization. Changes in the transportation sector are a key part of these efforts due to the large contribution of this sector to greenhouse gas and criteria air pollutant emissions, as well as overall energy usage. While a large amount of attention has been focused on shifts in the light-duty transportation subsector by means of improving efficiency and proliferation of electric vehicle powertrains, the heavy-duty sector is also in need of emissions reduction strategies. Multiple options exist for transitioning the urban bus fleet technology portfolio to contribute to emissions reduction goals. These include but are not limited to: 1) fuel-switching to lower-carbon, cleaner burning fuels such as natural gas, 2) deployment of all-electric battery electric buses –both short-range with roadway recharging and long-range with large battery sizes, and 3) deployment of hydrogen fuel cell buses. However, each of these options vary in their overall effectiveness in reducing different emission types over their life cycle, associated life cycle costs, ability to meet operational needs of transit agencies, and life cycle environmental footprint. In order for transit agencies to determine the cost-and environmentally favorable pathways for transitioning urban bus fleets to reduce emissions, information regarding the life cycle greenhouse gas and criteria pollutant emissions, costs, and environmental externalities such as water resource impacts for potential urban bus technologies must be provided.
Project Description: The first phase of this project focused on acquiring life cycle inventory data for different urban bus powertrain technologies by utilizing available life cycle databases and literature studies. For the second phase of the project, the research team modeled urban bus fleet operation to accurately capture operating energy needs and associated emissions in the context of powertrain characteristics and bus scheduling needs. The third phase of the project focused on utilizing the Brightway2 lifecycle assessment (LCA) framework in combination with a to-be-developed economic model for performing full LCA of different urban bus powertrain options to determine per-mile greenhouse gas emission, criteria pollutant emission, cost, and environmental footprint performance. The final phase applied the methodology to the Orange County Transit District (OCTA) as an example of the utility and applicability of the methodology. The project provided insight for the OCTA on the life cycle performance of different powertrain options on multiple criteria for use by state agencies and transit agencies in more effectively planning the transition of urban bus fleets to meet environmental objectives.