Abstract
The most comprehensive publicly available freight databases are the Commodity Flow Survey (CFS) and the FHWA’s Freight Analysis Framework (FAF). These two sources contain dollar value and weight of freight movements at high geographic levels, such as state or metropolitan areas. Due to the difficulty in obtaining freight data at lower geographies various practitioners and researchers have been suggesting to estimate freight models based on aggregate data.
Following these recent practices, a methodology to estimate a nationwide production and attraction models for U.S. domestic trade of goods is presented. To this end, a CFS’s data set provided by U.S. Census Bureau and composed of two-nonconsecutive year period (2002 and 2007) of movements of goods between U.S. states for 27 industry sectors was used. The state payroll by industry sector, obtained from the County Business Patterns of the U.S. Census, was the variable used to estimate freight generation models. The main objective of this paper is to analyze the temporal stability and predictability of the proposed aggregate models.
The results indicate that the payroll alone explains a significant portion of the freight production and attraction at the state level. However, such simplification in the model process did not result in reasonable predictions of freight for a future year horizon. It is recommended that time-dependent factors (e.g. variables related to changes industry productivity) affecting freight demand should be considered in the modeling process.