The Effectiveness and Safety of Traffic and Non-Traffic Related Messages Presented on Changeable Message Signs: Phase II

Project summary:

This project was the second phase of a study conducted to examine the effects of changeable message signs (CMSs) on driver behavior. That research, which was conducted as a baseline study to provide an initial understanding of their effects, found that some drivers decrease their speed in the presence of CMSs currently used by the Minnesota Department of Transportation (Mn/DOT), and drivers decrease their speed more in response to AMBER Alerts than to time-specific traffic-related CMSs. Further, the study revealed that the content of both the AMBER Alert and the time-specific traffic-related CMSs was not readily understandable to drivers, and this affected their response to the signs. This second phase of research compared the effects of newly developed messages (both a time-specific traffic-related message and an AMBER Alert) with data from the first phase of research. Comparisons focused on two areas: message comprehensibility and driver slowing behavior. In addition, given Mn/DOT's interest in knowing the effects on driver behavior of posting travel-time information on CMSs, another component of this study assessed the perceived value of travel-time information to the drivers who participated in the study. Real-world data associated with selected traffic incidents, collected at areas with CMSs by the Regional Traffic Management Center, was analyzed to assess the effects of messages on driver behavior. A fully interactive PC-based STISIM driving simulator was used to conduct two experiments which were similar to experiments in Phase I. Participants drove approximately 20 miles on a four-lane freeway before encountering target messages on CMSs: "Abducted Child/Tune To/Radio 88.5 FM." 71.7% of the participants could remember enough information to enable them tune to 88.5 FM, compared to 8.3% who could recall some vehicle information and at least five license plate letters and numbers from the Phase I CMS ("AMBER Alert/Red Ford Truck/MN Lic# SLM 509"). Some participants reduced speed on approaching the CMSs, suggesting similar reductions could occur in real world driving in free flow conditions. However, when traffic is congested speeds are typically slower, and drivers are less likely to reduce speed still further to read CMSs.