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CTRE
ISU Research Park
2901 S. Loop Dr.
Suite 3100
Ames, IA 50010

Phone
515-294-8103
Fax
515-294-0467

Webmaster:
mregenol@iastate.edu

Census Data

     The Census data provides other socio-economic data the might be useful in developing the model. A key piece of information is the population and income ranges. However, the Census data needs to be used with caution. The current aggregation of the data for small areas in Iowa can be over aggregated to make the data useless. For example, using the block groups, depending on the size of the location being examined, there might be only be two or three block groups that contain the entire community with a great deal of farmland surrounding the study area. The Census block groups might be a good method to determine TAZ structure for cities with a population greater than 6,000 (although this is just an estimate and all cities need to be examined on a city-by-city basis).






     This is illustrated in the following figures. The first shows the city of Clarksville, this community contains two block groups which encompassed the entire town and two rural block groups the made up the entire Clarksville area (each block group is identified in a different color).


















     The next figure shows the block groups for the city of Oelwein. Note that Oelwein has several block groups that would make appropriate zones for the network. Once again, the different block groups are shown in distinct colors.















     The information contained in the Census data that is potentially useful for trip generation include: population, income ranges and household occupancy. These datasets support trip generation following the procedure in the NCHRP #365: Travel Estimation Techniques for Urban Planning. Using the existing block group definition as traffic analysis zones and the associated data, a user can develop trip generation for three purposes: home-based work, home-based other and non-home-based.

     If the trip generation values are calculated based on a single purpose and use of the PhoneDisk CD-ROM, then the census data is not required.

The user should either go back to the Data Elements page or to the Site Map to continue.