Calibration of generalized cost models for road freight vehicles within an intermodal chain: an experimental application in Italy

In Italy an homogeneous modelling system for the analysis of freight transport on road and on other transport modality was developed. The incidence knowledge on freight transport time of different components is fundamental in many economics sectors. In literature different cost-flow models are specified and calibrated to calculate the travel time for road freight transport. The models are different in relation to several aspects: calibration, adopted attributes, estimate of travel time, geographic area of reference, data surveys. This determines the effectiveness in term of explanation capacity and statistics reproducibility, with a low level of reciprocal compatibility, therefore of validity in term of modelling system. For travel time the different approaches met in literature are in relation to the calibration relative to the links or to the OD pairs. Link cost functions are calibrated in order to define the relation between the link flow or density and link cost or speed. If we define a road link, on which we do the measures, we want to calibrate using measured link costs and measured link flows, the parameters that permit to correct the link cost functions. The parameters can be calibrated in aggregated way for each road category or in disaggregated way for each road link. In the OD pairs calibration the attention is on the path cost. In this case the cost in several OD pairs is measured and after the calibration of link cost function belonging to the paths are developed. Also in this case the calibration can be aggregated or disaggregated. This paper is focused on the calibration in the OD pair and the link cost functions for road freight trucks are specified and calibrated for different categories. Three main categories are individuated: freeways, extra-urban roads and other types. The dataset counts on about 40,000 interviews to truck drivers in the port of Messina. In fact, the truck trips from Sicily to other destination outside the island must cross the Straights of Messina. Data includes also departure locality and time, arrive time to the port of Messina. In this way we obtained the real (measured) time and cost on the paths. The estimation of cost-flow models for each category of links that compose the OD paths is done. The work was developed inside a national program of research SINAVE (SIstema di NAvigazione VEloce - System of Fast Navigation) in which an innovative system of freight is investigated. The project wants to give, by the acquisition and adaptation of specific knowledge, innovative technology solutions for the sea transport system, with particular attention on South-North sea freight transport in competition with road transport