The state-of-the-art variable message sign (VMS) systems have been widely used as a crucial means in the daily traffic environment to promote safe and efficient driving on highways. In addition, these overhead mounted VMSs play an important role in the Intelligent Transportation System (ITS) by displaying real-time information and advice about roadway and traffic conditions. Thus, a properly designed and displayed message on VMS is especially important to a motorist who has to detect, comprehend, and act on signage information while being occupied with the driving task. To this end, this book proposes a comprehensive human factors study, incorporating three approaches: driver questionnaire surveys, lab experiments, and field studies, to investigate various factors in VMS messaging and their impacts on a drivers understanding of and reaction to a message. The findings with a specific set of VMS features should help traffic engineers and highway management design VMS signs that could be noticed, understood and responded to in a more timely fashion. Safer and more proactive driving experiences could be achieved by adopting these suggested VMS features.