pictures to display is not based on this thinking. Finally, commuters were resistant to changing their times of departure or modes of transport based on current traffic information received prior to departure.
By consistently providing appropriately designed and delivered up-to-the- minute traffic information, one can improve short-term driver response to incidents and congestion and produce a long-term change in driver behavior that will increase the efficiency with which existing transportation facilities are used ( Haselkorn, Barfield, Spyridakis, Conquest, 1990). However, significant improvements in the level of congestion through delivery of traffic information can be achieved only if the mechanism for delivering that information is developed as an integrated system that is responsive to users' needs and perspectives. A great deal of information relating to the user subgroups was identified that reveals the importance of displaying accurate information to each group.
The results presented in this chapter support the central premise: Drivers cannot be considered as a homogeneous audience for motorist information. The method employed in this study has reinforced the idea that user groups have different behaviors and that identifying these differences will help to determine each group's use of and response to motorist information.
Targeting information for those motorists most likely to be affected does not mean that the same group will be targeted for all types of motorist information in all types of driving situations. Despite this focused approach, a single successful motorist information system can meet the needs of a wide range of motorists in varying conditions and stages of travel. This does mean, however, that a single integrated motorist information system must consist of carefully designed information modules targeted to address particular driving decisions of carefully studied and defined subgroups of receptive drivers.
As stated earlier, there are several subpopulations of motorists, each with unique user requirements that will need to be integrated for ITS. The three populations of potential users of ATIS--CVO have distinctly different preferences and requirements for information. Commercial drivers need to be aware of many more freeway restrictions and limitations. Dispatchers are very concerned about personal communication and the ability to convey sufficient information for assisting drivers in arriving at their destinations. There are many additional studies currently underway at the University of Washington to further define user requirements for other subpopulations. As more information about driver groups is obtained, more and better ways to design motorist information to meet the drivers' needs will be discovered.