Driver responses to graphic-aided portable changeable message signs in highway work zones

Portable changeable message signs (PCMSs) have been employed in highway work zones as temporary traffic control devices. Various studies showed that adding graphics to PCMS messages can provide advantages to traditional text messages, such as increasing legibility and improving the understanding of elderly drivers. This article synthesizes the findings of a two-phase research project aimed to investigate driver responses to graphic-aided PCMSs. Different text and graphic-aided PCMSs representing roadwork and flagger were set up in the upstream of highway work zones, and speed data of more than 2,700 vehicles were collected with a series of five speed sensors to determine vehicle speed reduction. Nearly 1,000 onsite driver surveys were performed to identify driver preference on the added graphics. The results discovered that graphic-aided PCMSs reduced mean vehicle speed between 13% and 17% and reduced the speed of passenger cars and trucks significantly differently depending on their locations in work zone. The results indicated that all drivers correctly interpreted the flagger graphic and two work-zone graphics, and suggested that 52% to 71% of drivers preferred to see graphics in PCMS messages. The findings also revealed that driver age did not have a significant impact on driver preference on PCMS message format.