This study seeks to quantify the effect of the University TRAX light-rail line on traffic near the University of Utah, providing data that can be used to shape future policies aimed at reducing traffic congestion, energy consumption, air pollution, greenhouse gas emissions, and parking costs. Travel demand models have long been used to evaluate the effects of transportation improvements on network travel flows and times, using four-step models or more sophisticated simulation studies. However, these are usually ex ante studies. Few ex post evaluations have been done, and the effects of transit have not been rigorously evaluated to support or refute the justification for subsidized transit. Such quantification is required for a comprehensive cost-benefit analysis. Our aim is to provide the first hard evidence of light-railÕs 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.