Efficient Interfacing of the Truck-to-ship Intermodal Grain Transfer System: Port of Houston

Agricultural transportation is often characBACKGROUND terized by seasonal and cyclical traffic flows that unfavorably affect the logistical efficiency of the marketing system. Congestion problems are an important link in the arise in the truck-to-ship intermodal grain export grain marketing system. Currently, 66 transfer system at the Port of Houston. Seaport elevators operate in the U.S. and these sonal peaks in truck-delivered grain receipts facilities are responsible for exporting approxicreate problems with efficient interfacing of mately 50 percent of the nation's annual wheat the port elevators' grain-receiving capacity and soybean production and 20-25 percent of and truck arrival patterns. During peak corn and grain sorghum output [14]. Because of the relatively small number of port elevators volume periods, the elevators' receiving capaan the rlare sv l number of port elevators city is inadequate; long truck queues develop volume of grain handled per unit and congestion or waiting occurs. Queues of 3f time, coordination with transportation is 4 miles are common during the peak receipt critical. When the port elevators' handling periods, whereas the facility may be idle for excapacity and the arrival rate of the transportended periods of offak time. tation agents are not synchronized, traffic congestion is rapidly generated. The truck conThe purpose of this article is to (1) quantify gestion addressed in this article occurs at the the magnitude of congestion cost associated Brownsville, Corpus Christi, and Houston with the seasonal surge in truck-delivered ports and is a result of Texas producers' seagrain at the Port of Houston, (2) estimate costs sonal grain sorghum marketing practices. of reducing this congestion to alternative During the past decade, Texas Gulf Coast levels, and (3) determine the least-cost level of grain sorghum production has stablizied at congestion-reducing investment or, converseabout 90 million bushels. Grain sorghum is ly, the optimum level of congestion to maxiharvested and marketed during July and mize efficiency. August because of favorable foreign demand and associated price-storage cost relationThe theory of queues provides a basis for ships. Approximately 70 percent of the produccalculating the nature and extent of congestion tion is shipped immediately to Texas Gulf port under conditions of fluctuating demands. elevators [5]. During peak activity periods, Queuing models have been used by agriculturtrucks must often wait 30 hours to unload beal and transportation economists to examine a cause queues include as many as 275 trucks [5]. wide variety of problems. Cox, Glickstein, and To attract truckers to this haul, rates are inGreene [3] applied queuing theory to determine creased to compensate for waiting times, i.e., necessary livestock unloading capacity at aucrates are bid up until truckers' return on the tion markets. Lu [10] used a queuing model to congested haul is equal to that earned on other determine optimum checkout facilities for a available noncongested hauls. In spite of the major food store chain. Queuing analysis was increase in truck rates, they are lower than rail used by Simmons [15] to resolve appropriate rates; primarily because of the proximity of the plant loading facilities for a fleet of milk distriproduction region to port locations and the bution trucks operating in North Carolina. Reassociated competitive advantage of trucks. cently, de Weille and Ray [4] and Wanhill [17] Annually grain elevators at the Port of analyzed optimum seaport capacity with use of Houston receive 44,000-46,000 truckloads of a queuing model. A recent Brookings Institugrain and soybeans or about 20 percent of the tion study employed queuing analysis to optitotal Port inflow. Historically, about one-third mize intermodal transfer systems for the deof the truck receipts have been in July and veloping transportation network in Columbia August. Within this eight-week period, there [8]. are typically three to four consecutive weeks of