Many currently existing generic transportation data models focus on the support of planning functions with very limited support for the needs of operations. Moreover, because of the dynamic nature of the transit network, highway based generic network models cannot be directly implemented by transit systems. In order to provide Internet transit trip planning service, an operational network data model must be developed that handles dynamic natures of the transit system. This paper presents an object-oriented Geographic Information Systems (GIS) data model that can handle time-variant transit networks. In this data model, the entire transit network and its components are modeled as space-time entities (objects) that have starting times, ending times and spans of lifetime. A time map component controls the creation and destruction of these objects. Therefore, in the process of network search, only active components of the system (i.e., with transit services available) are built into the network topology. This has greatly reduced data redundancy and enhanced network search efficiency.
Abstract