To address the need to minimize differential movement at railway transitions for joint high-speed passenger and freight routes in the U.S., this research study identified and studied three problematic bridge approaches near Chester, PA, along Amtrak’s Northeast Corridor line and another two on the N-Line mainline of Norfolk Southern near Ingleside, WV. The field instruments installed included multi-depth deflectometers for measuring track substructure layer deformations and rail strain gauges for measuring vertical wheel loads and quantifying tie support conditions. Analyses of both the track settlement and transient response data established the ballast layer to be the primary source of differential movement. Excessive vibrations within the ballast layer and significant gaps underneath the instrumented crossties recorded at the Amtrak bridge locations were linked to high-impact loads on the ballast as indicated by the significant negative displacements and the resulting crosstie oscillatory motion. The applied rehabilitation techniques included: (1) polyurethane grout injection and stabilization of existing ballast, (2) use of stone-blowing to add a thin layer of clean stone to the ballast under tie, and finally, (3) use of under tie pads to decrease pressure on the ballast and hence improve seating and load transfer beneath the tie.