Components of a Transportation / Land Use System

A transportation / land use system can be divided in three subcategories of models:

Land use models are generally concerned about the spatial structure of macro and micro-economic components, which are often correlated with transportation requirements. For instance, by using a set of economic activity variables, such as population and level of consumption it becomes possible to calculate the generation and attraction of passengers and freight flows.
Spatial interactions models are mostly concerned about the spatial distribution of movements, a function of land use (demand) and transportation infrastructure (supply). They produce flow estimates between spatial entities, symbolized by origin-destination pairs, which can be disaggregated by nature, mode and time of the day.
Transportation network models are trying to evaluate how movements are allocated over a transportation network, often of several modes, notably private and public transportation. They provide traffic estimates for any given segment of a transportation network.

To provide a comprehensive modeling framework, all these models must share information to form an integrated transportation / land use model. For instance, a land use model can calculate traffic generation and attraction, which can be inputted in a spatial interaction model. The origin-destination matrix provided by a spatial interaction model can be inputted in a traffic assignment model, resulting in simulated flows on the transportation network.