ECAT - Externality Cost Estimates are the estimated costs of highway use externalities including noise, air pollution, crashes, and congestion, broken into various degrees of specificity. For each category of externality the estimates include both the total annual cost (in millions) as well as dollars per vehicle mile traveled, and can be filtered by state, highway functional system, vehicle type, urban and rural. Additionally, every figure has a low, mid, and high estimate that embodies the uncertainty in the parameters and methodology used to construct the estimates. These estimates are useful for any analysis involving the value of negative externalities of highway use, such as benefit-cost analysis or impact analysis of highway projects.