Thermite welding is the most widely used technique for in-track welding or replacing a damaged part of a rail. This process produces a Welded Zone (WZ) and a Heat Affected Zone (HAZ) with inhomogeneous microstructures and hardness, resulting in lower mechanical, fracture and fatigue properties of the thermite weld compared with the parent rail. Tuskegee University developed (US Patent # 20140166766 A1) a new technology based on multi-pass Gas Metal Arc Weld (GMAW) for in-situ repair of railhead defects. In this technique, a defect is removed via machining a perpendicular slot or groove in the railhead leaving the web and base unaltered. Uniform preheating at a specified temperature is applied to the rail web under the slot before and during welding. GMAW passes are used to fill the slot using a weld material suitable for the parent steel rail to be welded. The weld heat inputs and other welding parameters are controlled to produce a weld with the desired microstructures. The proposed research focuses on investigating the metallurgical, mechanical, fracture and fatigue crack growth properties of the weld zone and the HAZ for both thermite welds and modified geometry and welding parameters of the Tuskegee GMAW repair technique, and to compare these properties with those of the parent rail. In addition, both conventional and inverse slow bend test on the modified GMAW and thermite weld repairs will be performed according to AREMA standard test methods. Comparison between the two welding techniques as far as rail safety is concerned will be made based on the fracture and fatigue damage tolerance associated with the weld zone and the heat affected zone. The fracture damage tolerance is defined as the resistance of the material (WZ and HAZ) to a crack under static loading, while fatigue damage tolerance is defined as the resistance of material (WZ and HAZ) to a crack under dynamic loading.