Intermodal freight transportation is one of the highest sources of revenue for North American freight railroads. However, intermodal trains are the least energy efficient in comparison to other types of trains and typically operate at higher speeds, thus creating significant aerodynamic resistance. The high resistance associated with intermodal trains results in significant fuel expenditures, and opportunities exist to reduce the aerodynamic drag through improved loading practices. An important step in the improvement of loading practices is gaining a greater understanding of how railroads load their intermodal trains and what metrics are used to evaluate loading configurations. Current North American railroad loading metrics consider equipment utilization, number of units, and/or total train length. However, these loading metrics do not account for the size of the well or platform and the size of the load placed in it. One proposed metric, slot efficiency, compares the difference between the ideal container/trailer size for the slot and the actual length of the load that is placed into the slot. Adopting this metric would enable railroads to better understand how their intermodal loading practices affect train energy efficiency. This paper reviews loading metrics used by North American railroads, identifies their strengths and weaknesses, and compares them to the slot efficiency metric using the AAR Aerodynamic Subroutine. The paper will also investigate potential challenges to improving slot efficiency of intermodal trains.