Optimum axle load limit on the trans west African highway – a case study of Ghana’s coastal corridor

Abstract

The Economic Community of West African States recently reviewed regulations on axle weights. Ghana rolled out its new regulation in January 2014. The allowable axle weights in the new regulation are much stiffer (e.g., the allowable single axle limit is now 11.5 tonnes compared to 13.5 tonnes, previously). Regional freight haulers contend that the new regulations make Ghana’s corridor less attractive to trade. However, the road agency sees it as a way of maintaining and extending road pavement life. The goal of this study is to find the optimum axle limit that is economically feasible to create a balance between road preservation and port competitiveness. Data collected on 47,959 individual trucks from July 2010 to December 2013 were analyzed. A calibrated Highway Development and Maintenance model for Ghana was used to estimate the total transport cost. The analysis showed that 19 % of trucks were overloaded, and footwear was the most frequently overloaded commodity. Overloading was common with all trucks, but 3-axle trucks experienced the highest extent of overloading. It was found that if the road agency maintains a high road maintenance standard (e.g., International Roughness Index = 3 m/km), then the optimum axle limits will be from 12-13 tonnes, 20-22 tonnes, and 28-29 tonnes for single axle, tandem axle, and tridem axle, respectively. However, at a low maintenance target (IRI = 7 m/km), the optimum limits need to be 12.5 tonnes and 18-19 tonnes for single axle and tandem axle, respectively, while the optimum tridem limit remains unchanged.