During 2001-2002, the proposed research team conducted a research project for the NCDOT focusing on determining the optimum strategy for sign inspection and replacement under different conditions to respond to pending retroreflectivity requirements the FHWA will likely impose (9, 10). Toward the end of that project, a simulation tool to quantitatively evaluate the effectiveness of different sign inspection and replacement scenarios was developed. The simulation 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 simulation estimates 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 simulation show that agencies that generally conform to the key assumptions made to build the simulation 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 with a program using visual inspection of each sign each year. The retroreflectometers appear to allow fewer deficient signs, while the visual inspection program costs are lower. Visual inspections every two or three years allow relatively high numbers of deficient signs to remain on the roads.
NCDOT may not feel comfortable using the simulation as it now exists due to one or more of the key assumptions that were made when building it. The purpose of this project is to remove those key assumptions and allow NCDOT to use the simulation with confidence. In particular, the model will incorporate the best possible sign deterioration functions available into the simulation, add the capability to analyze other types of signs besides yellow and red, and add data specific to the performance of NCDOT sign inspectors. With these additions, the simulation should be capable of saving the NCDOT hundreds of thousands of dollars per year in needless sign replacements, while insuring that motorists always see signs that meet minimum visibility standards.
The major objective of the research is to revise and expand the simulation of the effectiveness of sign inspection programs so that NCDOT can optimize its program. The main revisions necessary to allow NCDOT to use the simulation are to:Model the performance of NCDOT sign inspectors,Expand the simulation to include other sign colors besides yellow and red, andInclude the best sign deterioration functions.
The simulation model proposed herein utilizes various combinations of vandalism rates, deterioration rates, replacement cycles, and inspection methods to determine the costs of the sign management program and the number of signs that are not in compliance with retroreflectivity standards. Using this tool, the NCDOT can investigate various strategies to minimize cost, maximize the quality of signs on the road, meet the proposed new Federal retroreflectivity standard, and address liability concerns.
Use of the simulation program by NCDOT may show that some changes are necessary in the current program to realize the cost savings, safety benefits, and other benefits described above. The NCDOT may need to hire more inspectors, train inspectors better, buy higher-quality signs, obtain retroreflectometers, improve inspector training, or make other changes. The outstanding feature of this research is that the NCDOT would be able to precisely judge the payback periods from any of these types of investments.
