Various parameters affect the number of household trips, therefore it can be claimed that the first step in the modeling of trip-generation is identification of the most important of these parameters. In this research the effective parameters on trip-generation are determined and evaluated by using the rough-set approach as a modern mathematical method. The primary purpose of the present paper is to find the smallest sets of attributes having quality equal to the general quality of the defined characteristics in the information system. So, the number of parameters used in the modeling is reduced. To evaluate the results, the best algorithm of the defined attributes in the information system is identified by making use of the stepwise (stepwise linear regression) method and then compare the results with each other. The results of the research indicate that the rough-set theory has a better and stronger operational capability in identifying the effective parameters in trip-generation modeling. By taking advantage of these results, the amount of necessary data for trip-generation modeling is decreased and the speed and effectiveness of information processing are increased considerably.