The National Renewable Energy Laboratory (NREL) has introduced an enhanced version of its Transportation Technology Total Cost of Ownership (T3CO) tool to assist fleet operators in the transition to zero-emission vehicles (ZEVs). The tool focuses on simplifying cost calculations, providing a data-driven approach for fleet managers considering investments in battery-electric, hybrid, and hydrogen fuel cell vehicles. Switching from diesel to ZEVs offers significant cost savings, with lower fuel costs and maintenance expenses. However, challenges such as upfront capital costs and charging logistics may deter fleet managers. The T3CO tool addresses these challenges by offering insights into vehicle-specific costs and opportunity costs that are often overlooked. Key features of T3CO include batch mode capability for rapid analysis of multiple vehicle configurations, an optimization module for evaluating energy-saving features, and custom scenario planning for real-world variables. The tool's flexibility allows fleet operators to identify the most economical ZEV models that align with their operational needs. A unique aspect of T3CO is its consideration of opportunity costs, including factors like downtime during charging and capacity loss due to battery weight. This feature enables fleet managers to make informed decisions that balance costs with operational efficiency. T3CO supports phased decarbonization strategies, helping fleet operators identify cost-effective entry points for electrification without disrupting operations. By aligning with NREL's Fleet Research, Energy Data, and Insights platform, T3CO enables operators to anticipate future expenses and incorporate real-world data into their financial planning. The tool empowers fleet managers to make decisions based on actual use cases, fostering efficient and sustainable transitions to zero-emission transportation.