Train crews can't afford distractions or mistakes when operating 200-ton locomotives that are hauling dozens of cars and tons of freight. They must vigilantly juggle upcoming tracks, the train's speed, how the weight of the train will impact its safety, and monitor tracks in front of the train for dangerous conditions (like other vehicles trying to beat the train through a crossing). Hence, the Federal Railroad Administration (FRA) requires any system intended for use by train crew to undergo a human factors analysis.When the Interoperable Train Control consortium developed a positive train control system to support crews' adherence to movement authority limits (which specify the train's route and maximum speed) and to prevent unsafe movement, they asked Daedalus to perform the FRA-required human factors analysis. We conducted a formal usability analysis of the interface used by train crews during train operation, observed crews as they interacted with the system while operating trains on test bed tracks, and analyzed the cognitive workload imposed on crews by the system. We provided recommendations for improvement of the interface categorized by severity in terms of impact on the safety of the train, the cognitive workload imposed on operators, and the degree of potential operator frustration that could impact acceptance of the system.