Transportation data models traditionally are represented in Unified Modeling Language (UML). UML diagrams are intuitive for understanding transportation concepts and their relationships and thus provide standardized ways to construct transportation data models. Many UML models have been developed for this purpose. However, because UML does not consider semantics, sharing UML data is difficult. Reusing UML diagrams also is difficult. In contrast, Web Ontology Language (OWL) describes the semantics of ontology and thus is good for knowledge sharing and reasoning. OWL data are easier to share and better for performing logical inference. Unfortunately, no automatic method is available to transform data models from UML to OWL. A method to automate the transformation process is presented, using transportation data as a case study. Results indicate that transportation data represented in OWL have many advantages, including facilitated data sharing and inference. They also indicate that although many elements in UML can be transformed to OWL, some do not have OWL counterparts.