This study concerns the application of a disaggregate modal-split model in the persontripsurvey. In particular, this study forcuses on the determination of (1) the choice set for individual pair of zones, and (2) a method for estimating the trip-length of substitutable models. With respect to the aggregate process, Naive and Classification methods are unable to accountfor probabilistic aspcts of the disaggregation process. This paper proposes an Integrationmethod on the aggregation process.