Transport maintenance depots (TMDs) play a critical role in ensuring the reliability and efficiency of transportation infrastructure in developing countries like Tanzania. A mixed-methods approach combining data from surveys, interviews, and financial records was employed. Quasi-experimental techniques were utilised to assess system performance under different conditions. The analysis revealed that the implementation of preventive maintenance strategies reduced vehicle downtime by approximately 15% compared to conventional practices. The quasi-experimental design provided robust insights into the cost-effectiveness and efficiency gains associated with TMDs in Tanzanian transportation networks. Based on findings, recommendations include prioritising preventive maintenance training for depot staff and expanding coverage of TMD facilities across the country. Transportation Maintenance Depots, Quasi-Experimental Design, Cost-Effectiveness Analysis, Preventive Maintenance Strategies The maintenance outcome was modelled as $Y_{it}=\beta_0+\beta_1X_{it}+u_i+\varepsilon_{it}$, with robustness checked using heteroskedasticity-consistent errors.