The District of Columbia is preparing for the widespread adoption of connected, automated, and shared vehicles by analyzing the impacts of these technologies on the transportation system and the District as a whole in the DC AV Study. Understanding these types of impacts is difficult due to uncertainty surrounding the technologies themselves, but also about how people will adapt and adjust to these new transportation option. The work outlines a methodology for incorporating this uncertainty into the planning and forecasting processes using scenario analysis, using the complex real-world example of the recently completed DC AV Study. The methodology includes the development of comprehensive, realistic future scenarios, analysis methodology, key performance metrics, and detailed results for DC.