A second step for modeling involves finding a general representation that supports later multi-criteria evaluation
of routes. For private transport networks, the physical nodes and links can be represented as such in a model. For
public transport networks, it is more complex. In these networks, the time tables of services determine the transport
links; physical links may sometimes even be unknown to the modeler (e.g. metro). Therefore, the goal for modeling
multi-modal transport networks is to integrate all above factors together. Two available solutions are known in the
literature: one is the time dependent approach where time table events are handled as properties of links (the link
costs function); the other is the time expanded approach where time table events are separately represented as event
nodes (i.e., arrivals and departures) (Pajor, 2009). To create an integrated multi modal transport network, transfer
links between different modes have to be added when all subnetworks are ready. The resulting integrated network is
often referred to as a supernetwork.