Evaluation of overhead guide sign sheeting materials to increase visibility and safety for drivers

Overhead guide sign visibility must increase to improve driver safety on roadways. Two methods increase overhead guide sign visibility: sign illumination and use of retroreflective sheeting materials. This paper compares three types of retroreflective sheeting: Engineering Grade (type I), Diamond Grade (type XI), and High Intensity (type IV). A field experiment was conducted at night using licensed drivers to determine the optimum retroreflective sheeting material that increases sign visibility and legibility. Results showed that, of the three types of retroreflective sheeting, Diamond Grade (type XI) sheeting requires minimum illuminance to be visible, followed by High Intensity (type IV) sheeting. Cost analysis, including labor, maintenance, and material cost components of the three retroreflective sheeting materials, showed that High Intensity (type IV) could increase sign visibility and legibility at night for Departments of Transportation with limited budgets, consequently increasing driver safety on roadways.