Summary: A human factors study was carried out to help enhance ways to communicate with highway motorists through dynamic message signs (DMS). Overhead mounted DMSs have been increasingly used by highway authorities in the United States to present real-time traffic information and travel advice to motorists. It is critical to post sign messages that can be quickly and clearly understood by motorists, especially in high-volume traffic and construction/repair zones. Properly worded and formatted sign messages could spell the difference between comprehension and confusion. Message display factors investigated in the study include display effects, color schemes, wording, and formats. Two approaches were employed in this study. First, a questionnaire survey was developed to collect motorists' preferences regarding various message display factors. Second, a series of lab driving simulation experiments were set up to assess the effects of these factors and their interactions on motorists' comprehension of DMS messages. Study results suggested that static, one-framed messages with more specific wording and no abbreviations were preferred. Amber or green or a green-amber combination were the most favored colors. Younger subjects took less response time to the DMS stimuli with higher accuracy than older subjects. There were no significant gender differences.