The Federal Railroad Administration (FRA) and the Association of American Railroads (AAR) investigated the in-track performance of engineered-polymer composite (EPC) ties. This report summarizes the results from a revenue service test conducted by the Transportation Technology Center, Inc. (TTCI) between 2018 and 2021. Visual inspection identified two main types of defects often associated with EPC ties: center cracking and spike-hole cracking. In-track measurements indicated that the bending strain was well below the ultimate tie strength. Therefore, researchers concluded that fatigue failure resulting from dynamic cyclic loading caused both defects. The research team also found that differential thermal expansion affected the tie bending behavior and increased static track gage.