Chapter 6: Multi-Regional Input-Output Models for Freight Demand Simulation at a National Level

The simulation of freight demand at a national level has received a lot of interest in the literature: an exhaustive overview of approaches and models can be carried out through the state-of-the-art contributions provided, among others, by Daugherty (1979), Harker and Friesz (1986), Picard and Nguyen (1987), Zlatoper and Austrian (1989), Mazzarino (1997) and Regan and Garrido (2002). Normally, all national freight models are based on the integration of macroeconomic models, for the estimation of generation and spatial distribution of freight flows in connection with the economic system, and transportation models, for mode and route choice evaluation. Those dimensions are strictly connected since, on one hand, freight flows are a result of the economic interrelation between supply and demand of goods and services in different geographical areas and, on the other hand, localization of firms and selling markets depends also on transportation level-of-service attributes. Moreover, market conditions depend in turn on the performances of the transportation system, since the selling price of a good/service takes into account both production costs and transportation costs. Therefore, transport and economy are linked by several feedbacks and interrelations and, consequently, a proper simulation of those linkages represents the main challenge in modelling freight demand at a national level.