sector of the economy are used to calculate trade flows and later converted to the OD matrices of
transport flows using a spatial dimension and commodity’s value to volume ratios [. The mainstream
development of freight flows are on the basis of the traditional four-step approach. The first group of
models is “trip-based approaches” where the model deals with truck trips at the aggregate level without
addressing the level of commodity production and consumption. Another group is the “commodity-based
approach” which was proposed to overcome the above drawback of the trip-based approach. This
approach relies on the foundation that freight vehicle flows are the outcomes of the requirement for the
movement of commodities. Therefore, instead of directly generating a number of truck trips; the model
first calculates the amount of commodities’ consumption and production. Thus, this model needs an
additional step to convert commodity flows to freight vehicle trips. Holguin-Veras [2] provides a good
summary on the differences, advantages, and disadvantages of both approaches. Most models developed
in recent years are categorized into the commodity-based group.