摘要: |
Statewide models, including passenger and freight movements, are frequently used for supporting numerous statewide planning activities. Many states use them for traffic impact studies, air quality conformity analysis, freight planning, economic development studies, project prioritization, and many other planning needs. According to the databases from FHWA (2009) and Census Bureau (2010, 2012), the United States (U.S.) transportation system transported a total of 17.6 billion tons per year in 2011 to serve almost 117 million households and 7.4 million business establishments. The importance of truck demand has been increased in the statewide planning process because of its strong influence on the economy of the states and the nation overall. Truck is the dominant mode of freight transportation, with the industry hauling 11.9 billion tons in 2011, equating to approximately two-thirds (i.e., 67%) of all freight transported in the U.S. According to the Freight Analysis Framework (FAF) database, truck shares approximately 75% of the domestic freight shipments, and this trend is expected to continue until 2040. However, freight transportation capacity, especially roadway transportation, is expanding too slowly to keep up with demand. This growth imbalance could significantly contribute to congestion at highway segments, interchanges, and highway bottlenecks (i.e., locations that are physically narrow and/or congested) and hence are very susceptible to incidents and disruptions. Congestion is also caused by restrictions on freight movement, such as the lack of space for trucks in dense urban areas (FHWA 2008) as posted on the roadways due to height, length, width, weight limits, incident, or construction. |