UC Davis

The impact of transportation on the environment is a well-documented challenge facing several transportation industries today. To address this concern, several countries and states have created legislation or targets to transition various parts of their transportation fleets to zero-emission vehicles. One of these sectors undergoing an active transition is the public transit bus fleets, as zero-emission buses (ZEBs) are becoming more widespread in the US and around the world. However, transitioning from a traditional fleet to a ZEB fleet is a complicated and expensive process, with many decisions to make along the way. This research aims to model and optimize transit networks of ZEBs by using a mixed-integer linear program (MILP) model and optimizing based on total 12-year cost.Chapter 2 of this dissertation focuses on developing a method that is used to model transit networks. The MILP is developed and tested on a case-study network, with an energy uncertainty analysis performed to understand how vehicle energy use accuracy affects the model. The model reliably produced results consistent with forecasted implementations of ZEBs within the case study network, and that vehicle energy use had a substantial effect on the estimated best network architecture. Chapter 3 extends the model, making use of publicly available transit data to optimize 78 transit networks in the United States. For this version of the model, a focus was placed on the relationship between battery pack size and ideal supporting infrastructure at different infrastructure costs. Opportunity charging was found to be too expensive to be an economic solution, and that significant cost reductions would be required for make use of this strategy. What’s more, several networks required battery packs of sizes significantly larger than are available on the market today. Chapter 4 adds fuel-cell electric buses to the model, comparing the two technologies and considering the benefits of a mixed-technology approach to transitioning fleets to ZEBs. We found that such an approach has several benefits, being able to serve networks that an all-or-nothing approach to batteries and hydrogen otherwise couldn’t, while also costing less in terms of vehicles, infrastructure, and fuel. Although operational complications are not accounted for, this new paradigm of mixed-technology networks shows great promise in being a solution to the ZEB transition problem and should be explored further in future research.