Operations Research for Fleet Management Optimisation at Nigerian National Petroleum Corporation Downstream Logistics

Petroleum product distribution from NNPC depots to retail outlets across Nigeria's downstream supply chain is characterised by fleet underutilisation, unplanned vehicle downtime, and route inefficiency that contribute to recurring fuel shortages in inland cities. This study applies vehicle routing problem optimisation and preventive maintenance scheduling models to improve fleet management operations for a tanker fleet servicing the Mosimi, Kaduna, and Makurdi NNPC depots. GPS telemetry data from 45 tanker trucks collected over 16 weeks are analysed to estimate actual trip durations, idle times, fuel consumption, and failure frequencies. A time-window constrained vehicle routing problem model assigns tankers to outlet delivery sequences minimising total distance and ensuring delivery within operational windows. Preventive maintenance scheduling is modelled as a periodic maintenance problem minimising total maintenance and breakdown costs, with failure rates modelled as Weibull distributions fitted from historical service records. The optimised routing plan reduces total fleet travel distance by 18 percent and average delivery lead time by 9 hours. The preventive maintenance schedule reduces unplanned breakdown frequency by 34 percent compared to the reactive maintenance baseline. Combined savings are estimated at 1.2 billion naira annually. Keywords: vehicle routing, fleet management, NNPC, preventive maintenance, petroleum logistics.