A research project to determine the appropriate sign inspection and replacement procedure was
conducted at North Carolina State University and sponsored by the North Carolina DOT. The purpose
was to determine the optimum strategy for sign inspection and replacement under different conditions
to respond to the pending retroreflectivity requirements. This paper reports on a spreadsheet tool
developed to quantitatively evaluate the effectiveness of different sign inspection and replacement
scenarios. The spreadsheet was designed for yellow and red engineer-grade sign sheetings, and
takes into account sign vandalism and knock-downs as well as normal sign aging. The spreadsheet
provides estimates of the number of signs in place that would not meet the minimum retroreflectivity
standard and the cost of the sign inspection and replacement program.
The results from a number of trials of the spreadsheet show that agencies that generally conform
to the key assumptions made to build the spreadsheet should consider replacing all signs every seven
years, as that insures that no aged signs are in place at a relatively low cost. If total replacement
is not possible, an inspection program using retroreflectometers every three years appears very
competitive in its effectiveness with a program using typical visual inspection rates each year. The
retroreflectometers appear to allow fewer deficient signs, while the typical visual inspection program
costs are lower for a given vandalism rate. More conservative visual sign replacement rates do not
appear to offer distinct advantages, because typical replacement rates with visual inspections every
two or three years allow relatively high numbers of deficient signs to remain on the roads