Determining the Effectiveness of Graphic-aided Dynamic Message Signs in Work Zone

Portable changeable message signs (PCMSs) have been employed in highway work zones as an innovative temporary traffic control
(TTC) device in the United Stated for many years. The traditional message format on a PCMS 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 older drivers and non-English-speaking drivers, 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
used field experiments and driver surveys to determine the effectiveness of a graphic-aided PCMS on reducing vehicle speed and
drivers’ acceptance of utilizing a graphic-aided PCMS in the upstream of a one-lane two-way rural highway work zone. Field
experiment were conducted to compare the effectiveness of text PCMS, graphic-aided PCMS, and graphic PCMS on reducing vehicle
speed in a highway work zone in Kansas , and to develop regression models of the relationship between mean vehicle speed and
distance under three PCMS conditions. Driver surveys were conducted to evaluate drivers’ opinions on the implementation of a graphicaided
PCMS in the highway work zone. The findings showed that 1) using a text, a graphic-aided, and a graphic PCMS resulted in a
mean vehicle speed reduction of 13%, 10%, and 17%, respectively; 2) using a graphic-aided PCMS reduced mean vehicle speed more
effectively than using a text PCMS from 1,475 ft to 1,000 ft in the upstream of a work zone; using a graphic PCMS reduced mean
vehicle speed more effectively than using a text PCMS from 1,475 ft in the upstream of the work zone to the location of the second TTC
sign (W20-4 sign); 3) the majority of drivers understood the work zone and flagger graphics and believed the graphics drew their
attention more to the work zone traffic conditions; and 4) more drivers preferred the information to be presented in the graphic-aided
and graphic formats if the graphic-aided and graphic PCMSs were available.