In mining operations where trucks are the primary means of moving ore to processing plants and waste to dump sites, the efficiency of the production flow system is heavily influenced by the quality of haul roads. A thorough understanding of the requirements for constructing durable haul roads and predicting their behaviour, including deterioration patterns and maintenance frequency over their lifespan, is essential. Haul road quality directly impacts the performance of the transportation system, which can account for 45-55 per cent of mining costs. While equipment performance charts from suppliers offer insights into key indicators, such as truck speed, cycle time, and fuel consumption, these often assume deterministic conditions with a constant road quality. However, challenges arise when road design varies along its length or when poor design, inadequate drainage, and accelerated deterioration disrupt initial performance assumptions. Additionally, most mines feature road networks shared by multiple equipment types, including production and maintenance vehicles and light-duty traffic, leading to frequent interferences. Discrete-event simulation was applied to model these complexities in a phosphate mine in Brazil, providing a realistic view of fleet performance under varying conditions. Considering a theoretical base case, whose productivity was calculated according to the equipment's rimpull curves, and stochastic scenarios that address the impact of different rolling resistances (RR), it was verified that only the increase in RR promoted a significant loss in productivity of up to 5 per cent from RR values of 2 per cent to 6 per cent in the simulated scenarios. By comparing scenarios with and without best practices in haul road construction, the advantages of well-maintained roads and quantify the impact of road deterioration on equipment performance over time were demonstrated. This approach highlights the importance of maintaining steady road quality to achieve optimal transportation system efficiency, underscoring the benefits of sound haul road practices in minimising costs and maximising operational stability.