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The Upper Mississippi River (UMR) navigation system is a critical segment of the U.S. inland waterway transportation system. It extends 663 miles from Minneapolis, Minnesota, southward to the confluence of the Mississippi and Missouri Rivers near St. Louis, Missouri, and serves as a transportation artery for over 70 million tons of cargo annually (U.S. Army Corps of Engineers (USACE), 2004). The cargo is transported in barges that are lashed together in various patterns and pushed by a single powered vessel (tow boat, or TB). Just north of St. Louis, there is a series of five 600-foot locks (numbered 20, 21, 22, 24, and 25 in Figure 1) located between a pair of 1200-foot locks (numbered 19 and 26) with greater service capacity. The five smaller locks form a seasonal transportation bottleneck.
Figure 1. The Upper Mississippi River Navigation System
The locks are surrounded by different terrain and river conditions that affect the efficiency with which they can process the various configurations of barge tows. Further, they each experience different mixes of traffic. Vessels are processed at the locks using a first-come, first-served (FCFS or FIFO) policy, but some priority is granted to commercial vessels without barges and to recreational vessels. These types of vessels can usually be locked quickly between commercial vessels with large barge tows without causing inordinate delays for the latter. Under extreme operating conditions, the nominal FIFO policy may be waived with the agreement of commercial tow operators, and tows may be processed through a lock in sequences that allow local synergy to be achieved in the positioning, locking and clearing of queued vessels.
The Water Science and Technology Board of the Transportation Research Council at the National Academies of Science (2004) recommended that alternative traffic management policies be studied as a means of relieving the seasonal congestion in this section of the river. Alternative scheduling mechanisms have been shown to increase throughput in job-shop scheduling and other business environments (Naor, 1969; Su & Zenios, 2004; Rose, 2001; Nong et al., 2005). Ronen et al. (2003) postulated that better utilization of the UMR resources and improved services to commercial users could be achieved by employing intelligent scheduling mechanisms for river traffic and lock operations. In this paper, we describe how deterministic optimization and discrete-event simulation models were used in concert to explore the potential advantages of employing an alternative scheduling regimes and infrastructural changes.
Carroll (1972) and Carroll and Bronzini (1973) advocated discrete-event simulation to analyze the complex behavior of inland waterway systems. More recently, Dai and Schonfeld (1994); Kim and Schonfeld (1995); Martinelli and Schonfeld (1995); Ramanathan and Schonfeld (1994); Ting and Schonfeld (1998), (2001a), (2001b); Wang and Schonfeld (2002); Wei et al. (1992); Zhu et al. (1999), have investigated alternative scheduling schemes for lock operations and concluded that some form of priority scheduling should improve efficiency. Campbell et al. (2007) have described the ways that information technology can help in the implementation of alternative scheduling regimes and advocated computer simulation to study the effects of alternative scheduling rules and infrastructural changes. Smith et al. (2008) showed the importance of accounting for variations in traffic mix and intensity when testing alternative scheduling rules in a series of service facilities, demonstrated that system efficiencies can be achieved with a variety of local scheduling rules, and suggested that equity may be retained without degrading system-wide performance by giving higher priority to customers that wait longer than a specified interval.