Movement generation and trip distribution for freight demand modelling applied to city logistics

The quantification of the freight movements disaggregated by supply chain occurring in each traffic zone for the urban delivery of goods and that of the corresponding Origin-Destination trip tables is essential to evaluate the effects of any city logistic policy in terms of vehicle congestion and polluting emissions through the assignment of truck flows on the road network. In this paper we propose two innovative demand models: the first one for movement generation, the second one for trip distribution. The movement generation is addressed through an extension of the category index model, which takes into account the hierarchy in the classification system of the economic activities, thus avoiding aggregating the many existing classification codes into pre-specified groups. The trip distribution is addressed through an adaptation of the gravity model, which takes into account that deliveries are organized in tours. This approach has been successfully applied to the case of Emilia-Romagna Region in Italy, where an extensive campaign of surveys has permitted to calibrate both models for several towns and cities with various dimensions and vocations.