Control centers for IVHS systems are the focal point for collecting data from a wide variety of sources. These data can be in electronic form, such as the output from traffic detectors and computer systems or in anecdotal form such as police and radio reports or maintenance activities.There are two basic problems with handling this data; the data ages at differential rates and the quality of information varies according to the source. A video image of an accident scene is much more reliable than the output of an incident detection algorithm.Within IVHS control systems such data needs to be accumulated, organized and disseminated. In such systems, decisions need to be made for several thousand links every minute, 24 hours per day. This process has been termed data fusion. This paper describes the data fusion process and the manner in which it is applied in the Pathfinder and TravTek projects.