Effects of Tow Sequencing on Capacity and Delay at a Waterway Lock

Abstract

This paper presents several heuristic methods for sequencing tows through waterway locks, including locks with two dissimilar chambers. Two algorithms are proposed for obtaining good initial solutions. Of these, the shortest processing time first (SPF) algorithm gives priority to tows with lower processing time per barge, while maximum saving (SAVE) favors tows with the highest relative advantage at particular chambers. The resulting improvements in delays and capacity are evaluated by comparing these algorithms with a first come first served (FCFS) operation. Delay savings of up to 75.85% with SAVE and up to 79.73% with SPF are projected at congested locks. A pairwise exchange algorithm is used to improve the initial solutions obtained with SPF and SAVE. The improved methods, SPF with exchange (SPFX) and SAVE with exchange (SAVEX), further reduce the average barge delay. While SPFX does not improve much on SPF, SAVEX reduces average barge delay by up to 26.5% compared to SAVE. Among all these methods, SPFX yields the smallest barge delay (up to 79.8% less than FCFS). The delay savings can be even greater when upstream and downstream flows are unequal.