Port congestion has become a big challenge for many seaports in the United States (U.S.). There are multiple factors contributing to port congestion, such as the booming market of international container trading, limited space and capacity at a seaport, labor shortages, equipment failures, and supply chain disruptions (e.g., COVID-19 pandemic). Without appropriate management, port congestion will increase transportation costs, cause delays in goods movement and cargo delivery, reduce port operation efficiency, and lead to supply chain disruptions. Traditional strategies, such as infrastructure investment, truck appointments optimization, and party cooperation enhancement, have been implemented by ports for years, but the results are often unsatisfactory. To learn the needs of U.S. seaports and seek an efficient method for congestion relief, we develop a discrete event simulation model incorporating Container-on-Barge (COB) as an alternative transportation mode in this study. The simulation model mimics port operations involving COB and investigates congestion times at berth, yard, and gates. A case study on the Port of New Orleans (Port NOLA) is conducted to demonstrate the implementation of the simulation model and to evaluate the potential of COB for seaport congestion relief. The simulation results suggest that with a good level of COB development, the congestion at berth, yard and entrances of a seaport can be decreased significantly.