The FAA is sponsoring MIT Lincoln Laboratory to conduct human factors assessments of a prototype direct warning system aimed at preventing runway incursions called Runway Status Lights (RWSL). RWSL is comprised of Runway Entrance Lights (RELs), Takeoff Hold Lights (THLs), Runway Intersection Lights (RILs), and the enhanced Final Approach Runway Occupancy Signal (eFAROS), which provide autonomous information as a back-up to verbal air traffic control clearances. Human factors assessment has been essential to both the design and development of RWSL as well as on-going operational evaluations. This safety system has proven effective when both the technical performance and human response is correct according to the designated protocol. Since the commencement of the first field tests of RWSL in 2005, the user outreach, collection and assessment of feedback, and additional human factors assessment techniques have been key to the successful operational concept validation. Specific improvements resulting from system modifications based on human factors assessment will be discussed. Language: en