Most modern railways use Continuous Welded Rail (CWR). A major problem is the almost total absence of expansion joints that can create buckling in hot weather and breakage in cold weather due to the rail thermal stresses. In June 2008 the University of California, San Diego (UCSD), under the sponsorship of a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, began work to develop a technique for in-situ measurement of stress and detection of incipient buckling in CWR. The method under investigation is based on ultrasonic guided waves, and the ultimate goal is to develop a prototype that can be used in motion. A large-scale full rail track (70 feet in length) has been constructed at UCSD's Powell Structural Laboratories, the largest laboratories in the country for structural testing, to validate the CWR stress measurement and buckling detection technique under rail heating conditions well controlled in the laboratory. This paper will report on the results obtained from this unique large-scale test track to date. These results will pave the road for the future development of the rail stress measurement & buckling detection prototype.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.