The Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) required all states to develop and implement a congestion management system (CMS). ISTEA defines a congestion management system as a process of data collection and analysis. This process includes monitoring existing transportation system performance and evaluating strategies with the potential to reduce traffic congestion and improve mobility. The CMS, once implemented, will serve as a decision-support tool and an integral part of the transportation planning process. However, new analytical tools are needed to model and evaluate the potential benefits of congestion management as part of the CMS program. Under ISTEA, states and other government agencies began to recognize the positive benefits of congestion management in the planning process. As these benefits continue to be realized, a more thorough understanding of congestion and the need for better approaches to mitigate congestion will be achieved.