Abstract As an example of analysis of the energy impact of enlarging a river freight-transport system, we consider Locks and Dam 26 near Alton, Illinois, which is the principal bottleneck of the upper Mississippi River. A simple queueing theory model is developed to predict the average delay time prior to processing through the locks as a function of traffic growth rates. Estimates of the energy intensity of freight transport on the upper Mississippi are made from a theoretical model and compared with values published in the literature. The energy impact of the replacement of Locks and Dam 26 is assessed by combining the results of the traffic-flow and energy-intensity models. For a traffic growth rate of 2.5%/yr, the cumulative energy savings (during a 40 yr operating life) of replacing the current facility is nearly 20 × 1012 Btu. The economic value of the energy savings is 40–85% of the cost differential between repairing the current installation with no increase in capacity and the construction of an entirely new facility with a 100% increase in main locking chamber size.