{ "background": "Transport maintenance depots are critical infrastructure for road network reliability, yet systematic evaluations of their operational risk and reliability in West Africa are scarce. Existing assessments often lack rigorous, field-based methodologies to quantify the impact of targeted interventions.", "purpose and objectives": "This study aimed to develop and apply a randomised field trial methodology to empirically measure risk reduction and optimise the reliability of transport maintenance depot systems.", "methodology": "A randomised controlled trial was conducted across a representative sample of depots. Depots were randomly assigned to an intervention group, receiving a standardised package of procedural and physical upgrades, or a control group. Primary outcomes were measured using a composite reliability index (CRI). The treatment effect was estimated using a linear mixed model: $CRI{it} = \\beta0 + \\beta1 Treatmenti + \\gamma X{it} + ui + \\epsilon{it}$, where $ui$ denotes depot random effects. Robust standard errors were clustered at the depot level.", "findings": "The intervention yielded a statistically significant mean improvement in the CRI of 0.42 points (95% CI: 0.28 to 0.56, p<0.01) compared to control depots. A key theme from ancillary data was the pronounced effect on spare parts inventory reliability, which showed the largest component-wise gain.", "conclusion": "The randomised trial confirms that structured, low-cost interventions can substantially enhance depot system reliability and reduce operational risk. The methodology provides a robust framework for evidence-based infrastructure management.", "recommendations": "Infrastructure agencies should adopt randomised field evaluations to prioritise maintenance investments. The implemented intervention package should be considered for broader rollout, with particular attention to inventory management systems.", "key words": "reliability engineering, infrastructure management, randomised controlled trial, maintenance optimisation, risk assessment", "contribution statement": "This paper provides the first application of a randomised field trial to evaluate engineering interventions for transport depots in the region