The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation Model (GREET)
Measures the petroleum displacement and greenhouse gas emissions of medium and heavy-duty vehicles and off-road equipment.
"To fully evaluate energy and emission impacts of advanced vehicle technologies and new transportation fuels, the fuel cycle from wells to wheels and the vehicle cycle through material recovery and vehicle disposal need to be considered. Sponsored by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE), Argonne has developed a full life-cycle model called GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation). It allows researchers and analysts to evaluate various vehicle and fuel combinations on a full fuel-cycle/vehicle-cycle basis." 
Inputs and Outputs
Inputs include: The number and types of vehicles in a fleet.
Outputs include: Petroleum Consumption and Greenhouse Gas Emissions
This tool provides an easy way to compare various ways to improve fleet efficiency including fuel economy improvements and the use of alternative fuels. The tool provides estimates for common parameters such as fuel economy for various vehicle types, but allows the user to override those numbers for a more accurate estimate.
This tool will primarily be useful to those communities or organizaitons with a fleet of medium and heavy duty vehicles. This tool is not applicable to the civilian light-duty fleet.