Instead of focusing on any single element of a transportation procedure, process models seek to organize many elements into a model that defines a process by which some transportation planning or maintenance activity can take place. Perhaps the most widely known transportation process model is the Urban Transportation Planning System (UTPS) ?also known as the 4-Step travel demand models. By building UTPS models forecasts can be made about the demand for transportation resources under different conditions. It is important to note that process models are common and that transportation elements must be able to be associated in order to satisfy the needs of application developers who must implement such process models.[1]
The last general group of transportation models considered here are termed object models. Object models are those that seek to identify or enumerate as many transportation objects as possible and to logically organize them in such a way that they can be most profitably used. A notable effort to accomplish these goals is referred to as the Geographic Data Files (GDF). GDF has been developed in Europe and seeks to describe road and road related data. GDF specifies topological relationships and has several levels of description for different representations of objects.[1] Related to this type of object model is the idea of an 揈nterprise?GIS-T data model. Enterprise models recognize that many elements must be combined to provide an effective transportation system. Thus, enterprise models integrate network models and process models with cartographic entities. The relationships among them can then be defined.
Each of these models represents a structure that has been accepted by a group of
