Roads and traffic are a primary cause for habitat and genetic fragmentation, wildlife mortality, and reduced wildlife population resilience to climate change (Laurance et al. 2014; Brady and Richardson 2017; Seo et al. 2015; Bíl et al. 2017). Wildlife-vehicle collisions (WVC) can result in hazards, injury and death to drivers, injury and death of wildlife, and fragmentation of wildlife populations. State Departments of Transportation, wildlife agencies and others use evidence of WVC and other data to support decisions about WVC mitigation. One approach to reduce the population and species-level impacts of roads and traffic is to build infrastructural and other mitigation solutions. There are several ways to inform decisions about location, type and cost of mitigation options: 1) presence of high WVC densities or statistically-significant clusters posing driver safety and/or conservation threats; 2) proximity of wildlife observations, or collared wildlife, indicating a possible crossing area; 3) locations of genetic barriers, and 4) for migratory wildlife, such as mule deer, elk and pronghorn, known migratory pathways. Because the vast majority of wildlife species do not migrate or do not migrate on narrow, predictable paths, locations suitable for the few species that do migrate may not be suitable for other species. We developed a web-based tool (https://www.wildlifecrossingcalculator.org) to assist this decision-making process, based on economic benefits and costs associated with WVC and mitigation activities. The tool provides a portal for states and their partners to estimate benefits and costs and total value of proposed projects for WVC mitigation. The tool was based on the premise that “benefits” are the sum of avoidable costs (e.g., reduced crashes involving wildlife) and “costs” are the sum of response costs, such as constructed mitigation. We collaborated with transportation and wildlife staff from 5 US states (AZ, ID, MT, OR, WY) to elucidate goals for such a decision-support tool, develop wildlife values, estimate crash costs, and calculate costs for different types of mitigation. The workflow for the tool begins with the user creating a private or group account and uploading a WVC dataset, following format guidelines. The user defines a study area (e.g., state, project area) and selects either default wildlife and crash costs for their state, or enters new values. The user can also use default mitigation costs, or enter their own. The tool estimates the total costs (wildlife cost + crash cost) for individual WVC events, which can then be summed to a roadway segment (e.g., 1 mile section). The user can then compare the benefit of avoiding the costs of WVC with potential costs of mitigation. This benefit:cost fiscal comparison provides information comparable to other information used in transportation planning and could be critical to effective development of WVC-reduction programs.