A Study of the Visibility and Effectiveness of Fluorescent Retroreflective Traffic Control Signing in Work Zone Applications

Road works present a special challenge to both the driver and the traffic engineer. Work zone accident statistics attest to the need for safety improvements. One way traffic engineers have attempted to help drivers safely pass through work zones is to improve the advance warning to assure that drivers are aware they are entering a road works area. This research project was initiated to examine the effectiveness of fluorescent variations of standard retroreflective traffic signing colors. As part of a larger study on the role of fluorescent signing in traffic control, the authors examined the visibility of fluorescent and non-fluorescent work zone signing during the daytime and at night. They measured the detection distance, shape recognition, and color recognition of an assortment of full-sized traffic signs using 98 individuals in two age groups: 18-25 and 55-75. Additionally, in conjunction with the Norwegian Public Roads Administration, they conducted a traffic engineering field study of work zone approach speed as a function of advanced warning sign and speed limit sign color. The use of fluorescent orange signing has been steadily increasing in the U. S. in recent years, but there has been little quantitative research on its effectiveness. Because Norway also uses orange for work zone advance warning and detour signing, both fluorescent orange and ordinary orange were tested. Norway uses white with a red border for regulatory and warning signs in work areas. The authors tested fluorescent yellow-green as an alternate to white for these types of signs. Several other countries use yellow for their work zone signing. For this reason, fluorescent yellow and non-fluorescent yellow were also included in the visibility test portion of the research. As traffic congestion increases, road works crews are working both day and night; signs must be visible both day and night. Under both daytime and nighttime viewing conditions, the visibility of a traffic sign is determined primarily by its brightness contrast to the surroundings. Daytime photometric measurements of fluorescent retroreflective traffic signing materials have shown that fluorescent colors have a higher daytime luminance than do the corresponding ordinary signing colors. The results from this research show that daytime visibility of retroreflective signs is increased when fluorescent colors are used. The nighttime visibility distances of fluorescent and non-fluorescent retroreflective signs are equivalent. Significant differences between the two age groups were found in both the daytime and nighttime conditions. The field test data show significantly lower approach speeds to work zone areas where fluorescent signs were used. For these reasons, the authors recommend the use of fluorescent signing to improve safety in work zones.