Emergency care systems in sub-Saharan Africa face significant operational and methodological challenges. Robust evidence on system-level interventions is scarce, with few studies employing rigorous longitudinal designs to evaluate clinical impact. This study aimed to methodologically evaluate a randomised field trial design for assessing emergency care unit systems and to measure the clinical outcomes associated with a standardised systems intervention. A longitudinal, cluster-randomised field trial was conducted across multiple emergency units. Clinical outcomes for a cohort of patients presenting with acute trauma were tracked. The primary analysis used a mixed-effects model: $Y_{ij} = \beta_0 + \beta_1 X_{ij} + u_j + \epsilon_{ij}$, where $u_j$ represents random intercepts for units, with inference based on cluster-robust standard errors. The methodological evaluation confirmed the feasibility of the trial design in a resource-constrained setting. Clinically, the intervention was associated with a 17.3% reduction (95% CI: 9.1% to 25.5%) in time-to-critical-intervention for the trauma cohort. System-level coordination emerged as a dominant theme influencing outcomes. The randomised field trial design is a viable method for evaluating complex emergency care systems in this context. The implemented systems intervention demonstrated a statistically significant improvement in a key clinical timeliness metric. Future health systems research should adopt similar rigorous, longitudinal designs. Policy should focus on scalable system-level improvements that enhance inter-departmental coordination within emergency units. health systems research, cluster-randomised trial, emergency medicine, implementation science, trauma care, mixed-effects models This paper provides a novel methodological framework and empirical evidence for evaluating emergency care system interventions using a longitudinal randomised design in a sub-Saharan African context.