Transportation studies cover a wide range of topics consisting not only of planning, design and construction but also of policy, operations, economics, and impacts on society. This paper attempts a taxonomic classification of these studies and probes the extent of their scientific nature. First, what defines a discipline as scientific is introduced and the principles of scientific research are identified. The multidisciplinary aspects of transportation studies and the various focus areas are then discussed. Examples of broad areas of transportation studies are provided with a focus on inherent scientific principles. It is concluded that although the study procedures and the level of adherence to basic scientific principles may vary from one area to another, there are identifiable features that distinguish transportation studies as a distinct scientific inquiry, irrespective of the areas of application.