Impacts of Analysis Zone Structures on Modeled Statewide Traffic

Because a statewide transportation planning model covers a much larger area than an urban transportation planning model, land-use inventories and a household survey, which are often used to collect socioeconomic and traffic data for a UTP model, are prohibitively expensive for a STP model. The literature suggests alternatives of using the geography of census such as census tracts or block groups as Traffic Analysis Zones (TAZs) and using decennial Census for the socioeconomic data needed for statewide traffic demand modeling. The use of these alternatives raises new research questions for transportation planners. Which level of the census geography is better for statewide planning? Where should the centroids of TAZs be located given that the TAZs are heterogeneous in land-use activities? How much difference will the change of TAZ size and centroid location make in the results? Would the difference justify the extra effort in using more detailed TAZs and network? The primary purpose of this study is to determine how different TAZ structures and different roadway network details affect the ability of a STP model to replicate annual average daily traffic counts on the network. Idaho statewide traffic demand model is adopted as a case study. Results of this study can provide transportation planners a quantitative guide in selecting a zoning system for their statewide traffic demand models.