A DISAGGREGATE FREIGHT TRANSPORT MODEL OF TRANSPORT CHAIN AND SHIPMENT SIZE CHOICE

The field of freight transport modelling is relatively young compared to passenger transport modelling. However, some key issues in freight policy, like growing freight shares on the road, advanced logistics concepts or emerging strict freight transport regulations, have been creating increasing demand for freight transport models that satisfy the increased need for detail. (Tavasszy 2006). Especially regarding the increased detail needs, shortcomings in existing freight transport models are found. Firstly, mainly due to lack of disaggregate data in freight transportation, most existing freight transport models are aggregate models (De Jong 2007) rather than disaggregate models. This can result in a big loss of precision, particularly if aggregate groups of freight shipments are not homogenous with respect to their attributes. Secondly, logistics concepts, being a key issue in the development of freight transport, are insufficiently incorporated in freight models. Practically every freight transport model system proposed in literature or used in practice suffers from a lack of explicit treatment of logistics choices or explicit incorporation of a logistics costs perspective. Thirdly, although it has been widely accepted that decision makers make their choices of mode and shipment size simultaneously (Abdelwahab 1998), many freight transport models consider key decisions in an oversimplified sequential order, or ignore shipment size altogether.