Uganda Railways Corporation (URC) operates and maintains the railway line from Kampala to Malaba (single line of 251km) that is currently active. URC uses diesel-electric locomotives as mainline locomotives. Nalukolongo Railway Workshop (NRW) is the main workshop which does maintenance of locomotives and wagons. Proper maintenance system will ensure high availability of the railway network.rnThe maintenance concepts and intervals for all locomotives are, of course, dependent on the type of locomotive and what the Original Equipment Manufacturer (OEM) has prescribed for it. URC is therefore generally reluctant in determining its own maintenance strategies that would provide more efficient or effective use of maintenance resources and higher availability for the entire fleet.rnOEMâ€™s prescribe inspection and replacement moments dependent on time, cycles or working hours and they consider a certain usage pattern that is not necessarily applicable for URC. Moreover, inspection and maintenance periods also vary with the operating environment.rnMaintenance interval based on OEM is not reliable since actual operating conditions can differ thus need to adjust maintenance interval for a specific operating environment. Also, the application of preventive maintenance through experience is a conventional preventive maintenance practice. Through experience, no standard procedures are followed, thus itâ€™s not effective.rnIn this thesis, a step by step model for the â€œin house locomotive maintenance interval determinationâ€ is developed and tested. The model utilizes the cost per unit time function. The minimization of the total cost per unit time ï¿½ï¿½(ï¿½ï¿½) allows obtaining the optimal replacement interval. By using a graphical method on the cost per unit time function the optimal replacement time is obtained and the maintenance schedule is modified accordingly. The model is applied to improve the maintenance performance and hence increase the availability of the locomotives.