Determining the Effectiveness of Graphic-aided Portable Changeable Message Signs in Highway Work Zones

Abstract

Portable changeable message signs (PCMSs) have been employed in highway work zones as a temporary traffic control device in the United Stated for many years. The traditional message format on PCMSs is text-based, which has been found to have several limitations in recent studies, such as confusing drivers and delaying their responses during driving, being difficult to read for elderly drivers and non-English-speaking drivers, difficult to see under adverse viewing conditions, and having a short range of legibility. The use of graphic-aided messages on PCMSs has many advantages over text-based PCMSs based on a number of previous laboratory simulation experiments. This research project was conducted using field experiments and driver surveys to determine the effectiveness of graphic-aided PCMS in reducing vehicle speeds in the upstream of one-lane two-way rural highway work zones. Field experiments and surveys were designed and conducted in two phases. Field experiment Phase I was performed to compare the effectiveness of a text PCMS, two text-graphic PCMSs, and a graphic PCMS in reducing vehicle speeds in highway work zones. Through the driver surveys in Phase I, it was found that 12% to 21% of drivers were confused by the work zone graphic. Therefore, field experiment Phase II was conducted to compare the effectiveness of five graphic-aided PCMSs with the original work zone graphic and two redesigned work zone graphics (two alternative graphics) in reducing vehicle speeds. In addition, driver survey Phase II was performed to determine drivers' acceptance of the implementation of graphic-aided PCMS in highway work zones. Vehicle speed data and driver survey data were analyzed using a variety of statistical methods, including frequency analysis, linear and nonlinear regression models, hypothesis tests, independent two-sample t-tests, and Chi-square tests of independence. The major findings of this research project included the comparison of the effectiveness of text, text-graphic, and graphic PCMSs in reducing mean vehicle speeds in the upstream of highway work zones; the comparison of the effectiveness of graphic-aided PCMSs with the original and alternative work zone graphics in reducing mean vehicle speeds; and drivers' perception of graphics on PCMSs, acceptance of graphic-aided PCMSs, and preferences of message formats under different PCMSs. Based on the findings, recommendations were made for future research and implementation of graphic-aided PCMSs in the work zones. The results of this study provided valuable knowledge to government agencies and the transportation industry on how to regulate and utilize graphic-aided PCMSs in highway work zones.