This study assessed the feasibility of deploying mobile safety-sign robots to replace human flaggers in highway work zones and determined the optimal Dynamic Message Display (DMD) configurations. The study consisted of two phases. The first phase involved a pilot test on a test road in Yeoju, where the work zone conditions were replicated by following the highway work zone traffic management guidelines. Eight drivers participated in a pilot test. All four driving behavior indicators demonstrated improvements in driving safety under the robotbased scenario compared with the conventional human flagger scenario. The second phase adopted a Virtual Reality (VR)-integrated Driving Simulator (DS) to analyze the driver behavior across various DMD types. Six robot-based scenarios were designed by combining three DMD message types with two display sizes along with one baseline scenario based on existing guidelines for comparison. Twenty drivers participated in this experiment. A rank-based comparative analysis incorporating five evaluation indicators was performed to derive the optimal DMD display type. Scenario 3 (vertical ‘60’ display) and Scenario 6 (horizontal ‘감속60’ display, ‘Reduce speed to 60’ in English) were identified as the optimal DMD display types. These findings establish a foundation for the development of traffic management standards for safety sign robots in highway work zones.