Travel demand is manifested in space and time, and to model this one must represent the supply of transport infrastructure and services in some formal way. The most common way to achieve this is through the use of a network. This chapter deals with the concept of travel network and uses road networks, probably the most commonly used in modelling, as a starting point. The main components of a travel network are then described and the concept of link capacity and the relationship between level of service and delay explored. The chapter covers then the principles of travel assignment (the allocation of travel units to each link in the network) and considers the issues of congestion and equilibrium. In the final sections the discussion is generalized to cover other types of network: public transport, freight and modes different from road-based ones.
Abstract