Between September 2019 and June 2022, the Federal Railroad Administration (FRA) sponsored a research team from Sharma & Associates to model and test the torsional strength of a passenger car coupling system to understand the performance of coupling systems in train accidents and to enhance current specifications. The team designed a test fixture to apply a controlled torque to a complete coupling system comprising a coupler, yoke, draft gear, and draft sill, and developed a Finite Element (FE) model of the test fixture to assess its structural integrity and to predict the applied torque necessary for failure. The team identified two modes of failure, draft sill failure and coupler shank failure. The mode of failure was found to depend on the degree of constraint provided by the draft sill. Researchers found the results of full-scale testing agreed reasonably well with those measured in the FE model tests. Classical overturning calculations indicated that an applied torsional moment of 297 kip-ft, the lowest measured torsional capacity of the tested coupling system, would likely rollover a single rail car. Such an applied torsional moment will likely be near or beyond the yield capacity of modern car structures and would need to be evaluated on a case-by-case basis in possible future work.