Modal freight transport required for production of US goods and services
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and local agencies (CBO, 2007).Understanding the preferred methods of transportation, amounts of commodities shipped, and kinds of commodities
shipped can provide insight into the resiliency of the transportation system and project future infrastructure improvementsnecessary to create more reliable and efcient methods of transportation. International transportation of both goods andpeople deserves particular mention. International freight transportation to the US (in ton-km) was approximately equal
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Transportation Research Part E 47 (2011) 474489
Contents lists available at ScienceDirect
Transportation Research Part Edoi:10.1016/j.tre.2010.11.015ments in information and communications technology (ICT) and micro-scale management of businesses (such as just-in-time manufacturing) have increased the visibility and importance of logistics in the world economy (Womack et al.,1990; Klassen, 2000). At the same time, growing awareness of environmental issues such as climate change and air qualityhas made it more important that these increasingly intensive activities are performed in a sustainable way. Since transpor-tation contributes to 33% of US CO2 emissions and large portions of several criteria air pollutants (58% of NOX, 36% of VOCs,and 77% of CO), it is clearly important in efforts to promote environmental sustainability and green supply chain manage-ment (US EPA, 2004; Sheu et al., 2004). Transportation also represents a major investment of public funds, with over $45billion invested in transportation infrastructure by the federal government in 2006 and a comparable amount by stateInputoutput analysis
Transportation is ubiquitous in thin the delivery of nal goods. For exshields are shipped to auto manufaembodied transportation needed forsuch as fuel cost changes, trafc con2005). Over the past decades, supplmore complex, and more importantply chain of goods and services, in the shipment of intermediate inputs, as well as, in the case of automobiles, glass is shipped to windshield manufacturers, wind-rs, and autos are shipped to dealers where consumers buy them. Knowing theanufacturing and distribution of each product is useful when considering issuesn, and resiliency and security of the various modes of transportation (Smith et al.,ins and the logistics networks supporting them have become more global, faster,e US economy (US DOT, 2010; Meixell and Gargeya, 2005). Broad-scale develop-Modal freight transport required for production of US goods and services
Rachael Nealer , Christopher L. Weber, Chris Hendrickson, H. Scott MatthewsCarnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, United States
a r t i c l e i n f o
Article history:Received 28 May 2010Received in revised form 29 September2010Accepted 31 October 2010
Keywords:Freight movementCommodity owModal freight transportation
a b s t r a c t
In this paper we develop a model which approximates the upstream supply chains forembodied transportation in products. The sector with the largest embodied freight trans-portation in consumption is petroleum products followed by government services, con-struction, and food products. Overall, pipeline contributes 7% to the total embodiedfreight movement per sector, air transport is generally under 1%, water is 5%, and railand truck transportation are the most dominant modes (14% each) for domestic freighttransportation for the average sector. International water is the largest mode (60%) evencompared to domestic modes, and international air contributes less than 1%.
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R. Nealer et al. / Transportation Research Part E 47 (2011) 474489 475associated with transportation. Furthermore, future policies and means to improve efciency of transportation can be mod-eled at the national level with this research. In this work, we develop a model which approximates the upstream supplychains for embodied transportation in products. We estimate direct, rst tier, indirect, and total freight transport require-ments by mode for production in each of 428 interconnected US economic sectors. Here we dene direct transportationto represent the nal delivery of the purchased good to a nal consumer. Since service sectors do not produce physical goods,direct transportation would be zero for all service sectors. Service sectors account for approximately 100 sectors out of thetotal 428. First tier transportation represents transportation associated with a sectors direct inputs from its suppliers. Indi-rect transportation is transportation required in the upstream supply chain. Total, or embodied, transportation is the amountof transportation required to produce a nal product or service, and is the sum of direct and indirect transportation for asingle product or service. For example, the direct transportation requirements of an assembled automobile includes deliveryto the sales lot whereas total embodied transportation would include movement of the inputs needed at the assembly line(e.g., the windshield, tires, etc.), transportation to produce these parts from raw materials, transport of raw ores and mate-rials from mines, etc.
Using inputoutput analysis (IOA), we estimate total embodied ton-kilometers across the supply chain of products,similar to past work that has estimated total embodied energy use or emissions across the supply chain for various products(Facanha and Horvath, 2006; Weber and Matthews, 2008). Additionally, this model will quickly estimate direct andupstream transportation estimates for individual economic sectors, which can be further disaggregated into transportationrequired for the nal products each sector produces. The model will be available on the Internet at www.eiolca.net fortransportation and sustainability researchers who wish to pursue their own inquiries.
This paper rst discusses the model development, including a discussion of the data sources used and their correspondinguncertainties. The two allocation methods used to estimate the direct and indirect transportation for the economic sectorsare detailed in Section 2. The nal results are sensitive to the allocation method and show the sectors with the most embod-ied transportation. Section 3 displays the results of the model. Sections 4 and 5 conclude the paper with a brief discussion ofthe results, conclusion, and motivation for future work.
2. Methods and data
There are many studies that quantify the impacts of the direct transportation used to transport US products (Chapman,2007; Corbett and Winebrake, 2007; Vanek and Morlok, 1998). However there are few studies that include the supply chaintransportation embodied in products and services (Facanha and Horvath, 2006). Given the importance of transportation dueto environmental and infrastructure issues, and the growing importance of freight transportation, economic and environ-mental researchers have long tried to understand the interdependence of the productive sectors of an economy and the sup-porting transportation sectors (Leontief and Strout, 1963; Matthews et al., 2001; Williams and Tagami, 2003; Wilson, 1970).Two useful methods for such analyses are inputoutput analysis (IOA), an economic framework for modeling economy-widesectoral interactions, and life-cycle assessment (LCA), an engineering framework for analyzing the total cradle-to-graveeffects associated with processes, goods and services (Curran, 1996; Horowitz and Planting, 2006; Leontief, 1970; Vigonet al., 1993). The IOA methodology has been used in several studies to determine the embodied transportation in foodproducts, embodied water, and embodied discharge pollution for various US products (Blackhurst et al., 2009; Lave et al.,1995; Weber and Matthews, 2008). Weber and Matthews (2008) is fundamentally similar to the work done for this model,however here we consider the transportation requirements for all US products, not just embodied transportation in foodproducts consumed by households. We further rene the model by evaluating the importance of allocation methods. Thispaper focuses on the development of transportation-focused IOA methods that may later improve tools to assess the lifecycle energy and environmental impacts of produced goods.
The inputoutput analysis (IOA) framework, rst developed by Leontief (Leontief, 1970), is the core of the model. Thetotal output of an economy, represented by vector x, can be expressed as the sum of intermediate consumption, Ax, and naldemand, y:
x Ax y 1The square matrix of 428 by 428, A, is the economys direct requirements matrix with columns representing the fraction ofinputs purchased from other economic sectors for each of the 428 sectors and the rows representing the IO sectors. Whensolved for total output, x, this equation yields:
x I A1y 2where the inverted (I A) matrix represents the so-called Leontief inverse (Miller and Blair, 1985).ilities (e.g., strikes, infrastructure failure) and the response to increasing fuel prices can be useful for managing the riskIt is particularly important to understand the direct and indirect impacts of freight transportation because the totalembodied transportation is likely to be much larger than the direct transportation of a given nal product. Decision-makersmay thus underestimate the importance or impacts of transportation to their products. Understanding potential modal vul-tant as well, e.g., the emissions associated with international transport a