Prepared for American Association of State Highway and Transportation Officials (AASHTO) by ICF under NCHRP Project 25-25 Task 17, May 2006. This report identifies a total of 17 tools or methods that can be used to analyze the GHG implications of transportation projects. Existing tools are categorized into three groups: transportation GHG calculation tools, transportation/emissions strategy analysis tools, and energy/economic forecasting tools. These tools are designed to estimate travel and emissions impacts of specific types of transportation strategies, based on inputs about transportation programs or strategies (e.g., type of strategy, other parameters of specific strategies). Most of the analytical strength of these tools is in the estimation of travel impacts; the CO2 calculation procedures are generally very simple, and often do not account for complex implications of vehicle operating characteristics on emissions. These tools include the U.S. Environmental Protection Agency's (EPA) Commuter Model and the Federal Highway Administration’s (FHWA) Intelligent Transportation Systems Deployment Analysis System (IDAS).