Track conditions can change rapidly when operating in a revenue service heavy axle load environment. Because the assessment of track health for safe railroad operations is a fundamental priority for the railroad industry in North America, various track monitoring technologies, such as Track Geometry Measurement Vehicles (TGMVs) and unattended Vehicle/Track Interaction (V/TI) systems, are regularly deployed to determine whether track maintenance attention is warranted. To investigate the track condition monitoring differences between TGMV and V/TI technologies in a controlled environment where rapid tonnage is accumulated, Transportation Technology Center, Inc. (TTCI) engineers conducted a study on the High Tonnage Loop (HTL) at the Facility for Accelerated Service Testing (FAST) in Pueblo, CO. This study used TTCI’s rail-bound TGMV and a TTCI-developed Instrumented Freight Car (IFC), an autonomous car-based V/TI monitoring technology designed to run with the FAST train for continuous track condition assessment in a heavy axle load environment. In this investigation, funded by the Association of American Railroads (AAR) Strategic Research Initiatives (SRI) program, a total of six TGMV and IFC tests were conducted at different intervals with over 87.4 million gross tons (MGT) accumulated since the first track geometry baseline test was conducted. Compliance with track geometry standards was determined based on the Federal Railroad Administration (FRA) regulatory geometry defects for track Classes 1 through 5. Exception track locations were identified for the IFC when empirically derived, pre-set performance limits were exceeded. This paper both examines and contrasts the findings of the testing results of both the IFC and TGMV technologies as studied at FAST.