This chapter analyzes the role of users in enacting Intelligent Transportation Systems (ITS) functions and services. Preliminary evidence from recent demonstrations and market research studies is reviewed with a focus on the role of travelers in producing and using information about traffic conditions and traveler options. The potential for systems development is then considered with specific regard to alternative mode travel, flexible travel, emergency, and commercial services. Based on these findings, several directions and recommendations are made for creating the next generation of ITS systems that enhance user-based elements. Several areas for research and development are recommended, including integrating a wider range of market segments into ITS systems planning, developing a better understanding of how users drive complex systems, and creating new institutional partnerships for delivering innovative services.