Vehicle emissions are a function of many factors, including vehicle fuel efficiency, driving habits, and the type of fuel used. The estimation technique using this tool estimates the relative sensitivity of vehicle emissions to changes in each of these factors. The majority of these emissions are released from light-duty vehicles (LDVs), which include passenger cars, SUVs, and pickup trucks. For example, the matrix shows that a 1 percent increase in fuel efficiency would result in a 0.5 percent decrease in GHG emissions from LDVs. In contrast, a 1 percent increase in the use of alternative fuels would result in a 2.5 percent decrease in GHG emissions from LDVs. The matrix can be used to estimate the impacts of proposed changes to vehicle fuel efficiency standards or the adoption of alternative fuels. It can also be used to compare the relative climate change impacts of different transportation strategies.