12 The Journal of the South African Institution of Civil Engineering, which is distributed internationally, is a peer-reviewed, open-access journal licensed under a Creative Commons Attribution Licence (CC BY-NC-ND). Readers may therefore freely use and share the content as long as they credit the original creator and publisher, do not change the material in any way, and do not use it commercially. Copyright of this article remains with the authors. GODFREY AGORO is a professional civil engineer with a diverse work background spanning Kenya, Namibia and Djibouti. Having recently served as an international consultant with the World Food Programme in Djibouti, he brings a wealth of experience to the table. Holding an MSc degree in Civil Engineering from the University of Namibia, his 15-year career encompasses extensive consulting roles in both the private and public sectors, focusing primarily on transportation infrastructure such as roads, bridges and railway construction. Currently he dedicates his time to consultancy work, contributing valuable insight and expertise to the civil engineering industry. Contact details: Affiliation: PO Box 14242-00100 Department of Civil and Mining Engineering Nairobi University of Namibia Kenya PO Box 3624 E: godfreyagoro@gmail.com Ongwediva Namibia DR PETRINA T JOHANNES is a civil engineer with over 15 years of industry and research experience. She has authored more than 30 publications on performance evaluation of pavement materials, material specifications, product standardisation, and transport-related water resource management. She currently works as a Senior Lecturer at the University of Namibia and also serves on various technical committees and related bodies, including the Engineering Council of Namibia. She holds a BSc degree in Civil Engineering from the University of Cape Town, as well as an MSc and PhD in Civil Engineering from the University of Wisconsin Madison, USA. Contact details: Department of Civil and Mining Engineering University of Namibia PO Box 3624 Ongwediva Namibia E: pjohannes@unam.na DR ROBERT AMBUNDA is a transportation lecturer, consultant and the lead researcher in the Mobility Lab at the School of Engineering and the Built Environment (SEBE), University of Namibia. His research interests include areas around transport policy and regulation, resilient and equitable urban and rural transport systems, transport modelling, climate change and adaptation, and road safety. In his current post, he is responsible for teaching (undergraduate and postgraduate), and leading and coordinating research and commercial projects in transportation. He holds MSc and PhD degrees in Transportation Engineering. Contact details: Department of Civil and Mining Engineering University of Namibia PO Box 3624 Ongwediva Namibia E: rambunda@unam.na Agoro G, Johannes P, Ambunda R. Analysis of the extent of heavy vehicle overloading on Namibian trunk roads and evaluation of the effectiveness of existing mitigation measures. J. S. Afr. Inst. Civ. Eng. 2024:66(1), Art. #1499, 8 pages. http://dx.doi.org/10.17159/2309-8775/2024/v66n1a2 TECHNICAL PAPER JOURNAL OF THE SOUTH AFRICAN INSTITUTION OF CIVIL ENGINEERING ISSN 1021-2019 (print) | ISSN 2309-8775 (online) Vol 66 No 1, March 2024, Pages 12–19, Paper 1499 INTRODUCTION Overloading has been recognised as both a safety concern and a cost concern. Overloading occurs when a vehicle is loaded beyond its maximum legal weight (Yassenn et al 2015). Damage to roads as a result of overloading leads to higher maintenance and repair costs, and shortens the life of a road (Hornych 2015; Shahul & Prathap 2018). Consequently, these costs are carried by the road user if overloading is not controlled. Previous studies have shown that this condi- tion escalates when the control of traffic is poor (Rys et al 2016). It has been found that legally loaded heavy vehicles cause a relatively small amount of damage to road pavement structures, as opposed to overloaded heavy vehicles which are responsible for approxi- mately 60% of the damage to roads in South Africa (CSIR 1997). Roads are designed based on an assumed projected traffic load and volume. In the pavement design process, overloading is usually not taken into account and thus any heavy vehicle overloading dam- ages the structural design period (SDP) of a pavement (CSRA 1996). The SDP for roads in Namibia ranges from 7 to 30 years depending on the road categories. The SDP for the vari- ous road categories are as follows: Q Class A roads (SDP between 15 and 30 years) Q Class B roads (SDP between 15 and 25 years) Q Class C roads (SDP between 10 and 20 years) Q Class D roads (SDP between 7 and 15 years) (CSRA 1996; RA 2014). The Namibian road network consists of 8 250 kilometres of paved roads out of a total of 48 900 kilometres of road Analysis of the extent of heavy vehicle overloading on Namibian trunk roads and evaluation of the effectiveness of existing mitigation measures G Agoro, P Johannes, R Ambunda Overloading of heavy vehicles reduces pavement life and increases pavement life cycle costs. As part of Namibia’s strategy to control heavy vehicle overloading on the road network, weighbridge facilities have been constructed at strategic locations on primary routes (trunk roads). The study analysed the extent of heavy vehicle overloading on Namibian trunk roads, as well as the effectiveness of existing overloading mitigation measures. The dataset comprised heavy vehicle loading information from the year 2015 to 2019, from ten static weighbridge facilities. The parameters investigated include overloading magnitude, the effect of overloading on road pavement life, and the effectiveness of current overload mitigation measures. The results showed that 13.3% of the vehicles weighed were overloaded, with a compounded decrease in overloading of approximately 0.5% per annum. Despite the overloading decrease, the study found that the estimated road service life was reduced by as much as nine years over the study period. High levels of weighbridge avoidance and poor stakeholder coordination in mitigating overloading were identified. The study recommends deploying high-speed weigh- in-motion systems, an increase in fines charged for overloading offenses, and developing a demerit point-based system for habitual offenders to strengthen mitigation measures. Keywords: overloading, heavy vehicles, vehicle classification, axle loads, weighbridges