This report documents the findings of two simulation studies of air traffic controller reaction to the Precision Runway Monitor (PRM). The PRM is a new system for monitoring independent approaches, to closely spaced parallel runways. It consists of a radar which has higher accuracy and a faster update interval than the current system. The PRM radar is accompanied by a high-resolution color display which provides automated visual and vocal warnings to alert controllers of impending and actual penetration of a 'No Transgression Zone' between parallel runways. The studies, were conducted in order to determine the effects of key variables on controller reaction time and to determine controller opinion on system acceptability. Study I examined the use of the PRM when the runway separation was both 3,400 ft and 4,300 ft. Study II examined the use of the PRM when the runway separation was 3,000 ft. Real-time simulated approach blunders were presented to controllers, and measurements of their reaction times were recorded and analyzed. Independent variables studied included sensor update interval, runway separation, deviation angle, deviation range, flight path condition, approach blunder type, and controller experience level. In addition, controller opinions of the PRM were surveyed. Findings regarding the effects of each of the variables are reported. Survey results of controller opinion are reported. Recommendations for enhancing the realism of the simulation and recommendations of issues for future study are discussed.