Abstract for: Public Transportation Transitions Toward Zero-Emission Technologies: A Systems Thinking Approach

Transit fleet decarbonization is often treated as a technology selection problem, yet agencies that operate under comparable policy environments produce different outcomes. This paper addresses why similar agencies diverge and what structural mechanisms drive or constrain zero-emission bus adoption over time. A qualitative System Dynamics Causal Loop Diagram is developed at the transit agency level, integrating 32 variables across five dimensions: technology performance, operational feasibility, economic and infrastructure constraints, environmental impact, and governance and social dynamics. Variables were selected based on their existence in the literature and their suitability for future quantification. Eight feedback structures are identified and validated through polarity products and archetypes analysis. The CLD reveals four reinforcing loops, two balancing loops, and two causal chains. Five system archetypes are identified: Limits to Growth, Shifting the Burden, Success to the Successful, Fixes that Fail, and Eroding Goals, which explain divergent transition trajectories for transit agencies. Governance Coordination emerges as the primary leverage point, capable of simultaneously weakening balancing constraints and enabling reinforcing momentum. Decarbonization transition outcomes are not determined by the powertrain technology performance itself, but by which feedback structures dominate in a given context. The framework establishes a structural foundation for future Stock and Flow quantification and cross-city clustering analysis. Group Model Building validation with transit agency planners and utilities is planned as a next step. AI tools were used to support variable definition refinement and to improve the grammar and clarity of the manuscript.