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Rail transit track infrastructure and its components are expected to function as a system, and the performance and correct design of each component is critical to overall system behavior. A critical component in the transfer of load through the track system is the crosstie. Concrete is the dominant crosstie material choice for rail transit applications where safety and reliability of infrastructure are at a premium and maintenance time is often limited. Development and implementation of a structural design method that enables optimization of crosstie design for rail transit applications and loading environments will reduce initial capital cost and recurring maintenance expense; it is also important to characterize the loading environment at the wheel-rail interface. In this project, data collected at field installations throughout the US were used to quantify wheel-rail interface loads, concrete crosstie bending moments, and rail deflections under revenue service train passes. Field results indicated the need for development and application of a probabilistic design method for the flexural capacity of concrete crossties. A prototype crosstie for light rail transit infrastructure was designed, and a design process based on structural reliability analysis concepts was developed. New (proposed) designs are more economical, having a center negative moment capacity reduction of 50% for heavy rail transit. Further field instrumentation was installed on a heavy rail transit agency, in which wheel-rail interface loads were monitored to quantify rolling stock dynamic loading magnitudes and identify bad actor wheels.