Field Experiments for Comparing the Effectiveness of Graphics Displayed in a Portable Changeable Message Sign in Highway Work Zones

Abstract

The traditional message format on a portable changeable message sign (PCMS) is text-based, which has been found to have several limitations in recent studies. The use of graphic-aided messages on PCMSs has many advantages over text-based PCMSs based on a number of previous laboratory simulation experiments. To validate the effectiveness of graphic-aided PCMSs, a field experiment was conducted at a highway work zone in the summer of 2010. The results of data analysis indicated that between 12% and 21% of drivers got confused when the work zone graphic was displayed on the graphic-aided PCMS. Therefore, there was a need to improve the work zone graphic representation on the PCMS. Two alternative graphics were designed after the 2010 field experiment. The objective of this research project was to compare the effectiveness of two alternative work zone graphics displayed on a graphic-aided PCMS in reducing vehicle speeds in the upstream of a one-lane two-way highway work zone. Field experiments were conducted to collect vehicle speed data. In addition, driver surveys were performed to evaluate drivers’ acceptance on the implementation of a graphic-aided PCMS in work zones. The results of speed data analysis suggested that using alternative work zone graphics on the graphic-aided PCMSs could reduce mean vehicle speeds more effectively than using the original work zone graphic. The results of driver surveys revealed that all drivers successfully interpreted the two alternative work zone graphics in the work zone. Thus, authors concluded that the quality of graphic design had a significant impact on drivers’ understanding and acceptance of the graphic-aided PCMS in highway work zones.