This study seeks to quantify the effect of the University TRAX light-rail line on traffic near the University of Utah, providing quantitative data that can be used to shape future transportation policies aimed at reducing traffic congestion, energy consumption, air pollution, greenhouse gas emissions, and parking costs. Initial studies conducted by the Utah Transit Authority (UTA) on data collected by the Utah Department of Transportation showed that traffic near the university has fallen to levels not seen since the 1980s, even as the number of students, faculty and staff at the university has increased. What is less clear is exactly why this occurred. The university is the second-largest traffic generator in the state, and concerted efforts to encourage commuters to use transit to and from the university have resulted in a large number of commuters adopting transit as a primary means of commuting. A survey conducted in 2005 found that nearly a quarter of students, faculty and staff at the university used transit as a primary mode of transportation to and from campus. An audit ordered by the Utah State Legislature in 2008 found that transit passes issued to students, faculty and staff at educational institutions recovered just 8 percent of the cost of service. By comparison, other types of passes recovered an average of 24 percent of the cost of service. Determining the effect of the TRAX light-rail lines serving the University of Utah campus on traffic along parallel arterial streets will make it possible to quantify the savings in traffic congestion, energy consumption, air pollution and parking costs such subsidies provide, and allow a full evaluation of the partnership between the university and the UTA. Travel demand models have long been used to estimate and evaluate the effects of transportation improvements, like LRT investments, on network travel flows and times as part of long-range planning studies, using four-step models or more sophisticated urban simulation studies. However, these are usually ex ante studies. Few ex post evaluations have been done, and in this sense, the effects of transit on traffic volumes and associated energy consumption and air pollution have not been rigorously evaluated to support, or refute the justification for subsidized transit. Such quantification is required for a comprehensive cost-benefit analysis. Transit is assumed to reduce traffic congestion, and alleviate the negative impacts of congestion. The introduction of TRAX light-rail service to the university provides a quasi-experiment from which we can quantify the before-and-after impacts of transit. Our aim is to provide the first hard evidence of light-rail’s impact on traffic in a travel corridor, to quantify the associated savings on energy consumption, air pollution, and parking costs, and to compare cost savings to transit subsidies.