CREATING SYNTHETIC BASE-LINE POPULATIONS

To develop activity-based travel models using microsimulation, individ ual travelers and households must be considered. Methods for creating baseline synthetic populations of households and persons using 1990 ce nsus data are given. Summary tables from the Census Bureau STF-3A are used in conjunction with the Public Use Microdata Sample (PUMS), and I terative Proportional Fitting (IPF) is applied to estimate the proport ion of households in a block group or census tract with a desired comb ination of demographics. Households are generated by selection of hous eholds from the associated PUMS according to these proportions. The ta bles of demographic proportions which are exploited here to make house hold selections from the PUMS may be used in traditional modeling. The procedures are validated by creating pseudo census tracts from PUMS s amples and considering the joint distribution of the size of household s and the number of vehicles in the households. It is shown that the j oint distributions created by these methods do not differ substantiall y from the true values. Additionally the effects of small changes in t he procedure, such as imputation of additional demographics and adding partial counts to the constructed demographic tables are discussed in the paper.