Life-Cycle Cost Modelling of Access Roads to South Sudan Oil Fields Under Extreme Climatic Conditions

The access road network serving South Sudan's oil fields in Unity, Jonglei, and Upper Nile States constitutes critical energy-sector infrastructure whose deterioration under extreme tropical rainfall, flooding, and overloaded tanker traffic imposes cascading economic losses on oil production revenues, logistics operators, and road users. Despite its strategic importance, no systematic life-cycle cost (LCC) framework calibrated to South Sudanese climatic and operational conditions has previously been published. This paper develops and applies such a framework, integrating the Net Present Value (NPV) approach with HDM-4 pavement performance modelling, Vehicle Operating Cost (VOC) estimation, and Monte Carlo simulation of climatic uncertainty across five oil logistics corridors totalling 1,865 km. Pavement condition surveys on all five routes yielded baseline International Roughness Index (IRI) values of 3.2–6.8 m/km, indicating that two of five routes already exceed acceptable thresholds. Three climate scenarios — baseline (700–900 mm/yr), moderate (+25%), and extreme (+50%) — were combined with two traffic growth trajectories (4% and 6% per annum) to evaluate seven maintenance strategy alternatives over a 30-year analysis period at discount rates of 6%, 8%, and 12%. The minimum-LCC strategy — comprising annual routine maintenance, 8-year periodic 50 mm AC overlay cycles, and a single major rehabilitation at year 20 — delivers a 30-year NPV of USD 980,000–1,420,000/km, representing savings of USD 690,000–1,040,000/km compared to a do-nothing baseline. Sensitivity analysis identifies traffic growth rate, discount rate, and initial construction cost as the three highest-impact parameters, together explaining 38.7% of total NPV variance. An LCC optimisation surface derived f