Effective highway signing is an important component of driver decision making, comfort, and safety. Like many agencies across the country, overhead sign lighting has been used by the Florida Department of Transportation (FDOT) to improve visibility. However, the availability of newer and more efficient retroreflective materials has created a new challenge for state transportation agencies going through sign upgrade programs and considering the need for sign lighting. FDOT initiated this study to investigate whether high intensity reflective sheeting can be used to replace overhead sign lighting. Field data was collected to assess the conditions of Florida signs in terms of the MUTCD minimum maintained retroreflectivity levels. In addition, a luminance computation model was developed to calculate sign legend luminance under various situations, including different sign lighting technologies, different geometrics and sign locations, and different amounts of sign dirt and sign aging. By comparing the calculated luminance of a specific sign at a specific situation with the legibility luminance levels required by older drivers, sign lighting needs were assessed. A life-cycle cost spreadsheet was developed and used to calculate the cost of replacing the current sign sheeting in Florida with high reflective sheeting and the cost of installing/upgrading sign lighting. Based on this analysis, we found that under the conditions considered (either on straight and flat roadways or horizontal curves, in rural areas or urban areas), the most cost effective approach to maintain overhead guide luminance is to use (installing or replacing with) induction or LED luminaires. The results also indicate that a viable alternative (in terms of maintaining luminance and being cost effective) would be to use either Type VIII or Type XI legend sheeting materials and forgo sign lighting. For Type XI sheeting materials, sign lighting would be needed along horizontal curves in rural areas with radii of 880 ft and horizontal curves in urban areas with radii of 2500 ft or less. (Author/publisher)
Abstract