A typical large freight railroad in the United States owns between 4,000 to 8,000 locomotives, each costing millions of dollars. As per Federal Railway Administration (FRA) regulations, every locomotive must be sent to a shop for quarterly maintenance (Q) every 92 days. If a locomotive cannot reach a shop by then, it becomes past-due-Q and is required to be taken out of service. Thus, is it the locomotive manager’s responsibility to direct locomotives to shops just-in-time so that the number of locomotives arriving at a shop on a daily basis is consistent with the shop’s capacity and capabilities. Many locomotives at CSX Transportation were becoming past-due-Q before reaching shops, hurting locomotive productivity. The company asked Optym to build a real-time decision support system to route locomotives due for quarterly maintenance at shops to reduce the number of past-due-Q locomotives.