Scheduled preventive maintenance is required to preserve waterway locks and ensure satisfactory service in waterway operations. Because delays to waterway users usually increase during periods of lock maintenance, shippers may change departure times or switch to a different transportation mode. The analysis of variations in waterway traffic due to lock maintenance is a challenging task. This paper analyzes the cost structures of waterway and rail transportation and develops three waterway demand models on the basis of different user behavior assumptions. Numerical testing is conducted to verify the models. The results of the analyses show that these models, grounded in economics, traffic flow theory, and queuing models, can capture the effects of demand changes over time.