Two levels of efforts advance the world: theory and application. Their highest levels of development are called "the state of the art" and "the state of the practice", respectively, with the latter typically lags behind the former. This is particularly true with traffic simulation where applications are more concerned with reliability, operability, adaptability, and availability. The state-of-the-art traffic simulation theories and models have been documented comprehensively while literatures on the state-of-the- practice applications are relatively sparse. This paper illustrates the perspective that industry typically takes on how to conduct traffic simulation by means of an example application: I-85 traffic study. Background information is given first, which is followe d by general considerations such as simulation software selection and data requirements. A step-by-step procedure of model development is next, together with issues encountered during the development of the base model and strategies of solving these issues.