Trip generation rates for large elevators - A North Dakota case study

Large grain elevators are major sources of truck traffic in many areas. Shuttle trains, a recent railroad innovation, have further concentrated truck deliveries at larger elevators. These facilities-which have not been analyzed in previous trip generation studies-pose issues such as large truck access and pavement design. In this paper, elevator trip generation equations are estimated from detailed facility, land use, and highway traffic data in North Dakota. A trip attraction equation is used to explain the effects of elevator storage capacity and side track capacity on elevator throughput. Elevators are classified on the basis of track capacity as shuttle train, unit train, and multicar. Shuttle-train elevators typically consign 110-car trains, while unit-train elevators consign 50- to 100-car trains. The analysis shows that large shuttle-train elevators may generate 35,000 to 40,000 loaded and empty truck trips per year. A large unit-train elevator may generate 20,000 annual trips. The trucks are usually a mixture of combination five-axle and single-unit trucks. On average, each truck generates 1.04 equivalent single-axle loads on flexible pavements. Thus, a large facility may generate much of the traffic load experienced by pavements in the area. Moreover, truck deliveries to elevators exhibit seasonal variation. Approximately 15% of the annual volume is delivered during the peak month. Thus, a large shuttle facility may generate 225 trucks per day during the peak harvest month.