The U.S. Department of Transportation study "What Have We Learned About ITS?" is a synthesis of the national experience with implementing ITS through the year 2000, with a goal of more effectively planning the future of the National ITS Program. This synthesis examines which ITS technologies and applications have been successful, which have not, and those for which more information is needed to make a judgment. The seven areas included within the scope of this study are as follows:
- Freeway, Incident, and Emergency Management, and Electronic Toll Collection (ETC)
- Arterial Management
- Traveler Information Systems
- Advanced Public Transportation Systems
- Commercial Vehicle Operations (CVO)
- Cross-Cutting Technical Issues
- Cross-Cutting Institutional Issues
Adaptive signal control systems use algorithms that perform real-time optimization of traffic signals based on current traffic conditions, demand, and system capacity. Adaptive control software adjusts traffic signal splits, offsets, phase lengths, and phase sequences to minimize delay and reduce the number of stops. The extent of benefits depends on several factors including the number and spacing of intersections, the size of study area, demand patterns, levels of nonrecurring congestion, and the type of adaptive control.
Mobility benefits were realized from U.S. deployments of adaptive signal control systems in Los Angeles, California; Broward County, Florida; Newark, Delaware; Oakland County, Michigan; and Minneapolis, Minnesota. Delay reductions ranged from 19 to 44 percent. In Los Angeles, Broward County, and Newark adaptive traffic signal control systems decreased travel times by 13 to 25 percent.
Integration of arterial traffic management systems across jurisdictions can yield delay reductions by providing a seamless travel corridor. Interconnecting previously uncoordinated signals and providing optimized timing plans with centralized control can reduce travel time. For example, when several jurisdictions in Denver, Colorado worked together to coordinate signals on arterial corridors, travel time reductions ranged from 7 to 22 percent. Integrating arterial traffic management systems with transit and emergency operations can reduce emergency vehicle travel time and reduce delay for transit vehicles. Integrating arterial, freeway, and incident management systems in San Antonio, Texas led to travel time reductions of 20 percent during major incidents.