TRB’s Airport Cooperative Research Program (ACRP) Synthesis 2: Airport Aviation Activity Forecasting examines how airport forecasts are used and identifies common aviation metrics, aviation data sources, issues in data collection and preparation, and special data issues at nontowered airports.  The report also explores available forecasting methods, including the primary statistical methods; market share analysis; econometric modeling; and time series modeling.  In addition the report reviews forecast uncertainty, accuracy, issues of optimism bias, and options for resolving differences when multiple forecast are available.