Under the sponsorship and support of the Federal Railroad Administration (FRA), Transportation Technology Center, Inc. (TTCI), with participation from the original equipment manufacturer (OEM) of advanced nondestructive evaluation (NDE) equipment, NDE service providers, and other research institutions, conducted a feasibility study of applying advanced NDE methods to detect and characterize weld defects in railroad tank cars. Researchers evaluated the performance/capability of various state-of-the-art advanced NDE techniques for fatigue crack detection and characterization in railroad tank car butt welds and fillet welds. The team determined that advanced NDE methods could detect toe fatigue cracks with acceptable signal-to-noise ratio (SNR) while demonstrating challenges with accurate flaw sizing. Further, based on the false positive results obtained from this study, the team found that detailed attention and efforts are required to reduce the false positive rate.