Rail internal defects have been one of the leading causes of track-related accidents. Rail internal defects can reduce cross-sectional area and introduce stress concentration. Moreover, they can develop with normal, rapid, and sudden growth rates. If left undetected, internal defects can result in broken rails, train accidents, and derailments, where sudden rail rupture can occur without warning. Accurate and reliable rail flaw detection is therefore critically important for improving safety and reliability and minimizing the risks of accidents induced by rail internal defects. Nondestructive evaluation (NDE) techniques, including roller search unit (RSU), ultrasound A-Scan, and phased array, have been employed to detect rail internal defects but their performance or accessibility has been limited. This project will develop a new technology using a newly identified wave propagation phenomenon  (local resonances in rails) for rail defect detection.  These local resonances feature highly localized energy and signature frequencies that are governed by the geometry and material properties of a rail. These local resonances were found to be sensitive to internal defects over the full rail cross-section and are easy to measure. A low-cost contactless acoustic sensing prototype will be developed that would generate local resonances in rails. These resonances will provide flaw detection capability over the full rail section. The prototype’s sensing configuration will be simple and robust and, compared with existing NDE techniques, it will not require sophisticated/expensive sensors or data acquisition systems. It will combine fast data collection with efficient data processing to produce timely critical damage alert. If successful, the project is expected to have a significant impact of the current state of practice for accuracy and practicality with regard to determining the presence and severity of internal rail defects.