TRB's Conference Proceedings 36, Performance Measures to Improve Transportation Systems: Summary of the Second National Conference are the proceedings from a conference held on August 22-24, 2004, in Irvine, California. The purpose of the conference was to explore the implementation and use of performance measures and to discuss how to monitor the impact of performance measures on the delivery and quality of transportation services. The proceedings include summaries of presentations made in each conference session and of resource papers. These summaries highlight a variety of agencies' experiences with the use of performance measures and identify research that could improve the use of performance measures. The resource papers prepared for the conference are also included in the proceedings.