Under the Association of American Railroads’ (AAR) Strategic Research Initiatives (SRI) program, in cooperation with BNSF Railway and commercial technology suppliers, MxV Rail (formerly TTCI) conducted a year-long, in-service assessment of locomotive undercarriage thermal inspection systems (LUTIS), also known as “in-track thermal detectors.” Through this assessment, MxV Rail provided evaluation support and visibility of the results to the industry. The assessment was conducted by installing thermocouples (TCs) on the major driveline components of three different motor styles of BNSF locomotives: a GE DC traction motor (TM), a GE AC TM, and an EMD AC TM. Data loggers were configured to record the real-time temperature information on a continuous basis for every TM on each locomotive. This Technology Digest discusses analysis of the on-board TC temperature readings collected during the evaluation period. BACKGROUND The LUTIS is a relatively new concept suggested by the railroads for monitoring locomotive major driveline components that…