Field Investigation of Highway Sign Damage Rates and Inspector Accuracy

sign replacement, visual inspection. Immaneni, et al. 2 The overall purpose of the research study reported here was to create a simulation model that could provide the NC Department of Transportation (NCDOT) with recommendations to improve their sign inspection and replacement procedures. The research reported in this paper focuses on two key factors built into the model: 1) the rate at which signs are damaged beyond usefulness based on natural or man-made causes, and 2) the accuracy rate of visual sign inspections based on retroreflectivity. To explore those factors, the research team conducted night time rides with sign inspectors in 5 of the 14 NCDOT divisions. During subsequent daytime rides along the same routes the research team measured sign retroreflectivity to allow estimation of sign deterioration and inspector accuracy rates. Data were collected for white, yellow, red, and green signs and for sheeting Types I and III. Two key results emerged. First, about 2.3 percent of the inspected signs (per year) were damaged to the point of needing replacement. Second, inspectors did not reject a large percentage of signs that had retroreflectivity values below the proposed minimum FHWA standard