The major objective of this study is to develop and analyze systematic and efficient sign replacement strategies for the North Carolina Department of Transportation (NCDOT). The research team developed a microscopic simulation model to study sign replacement strategies and analyze the trade-off between sign cost and condition. This model simulates sign damage, blanket replacement, grace period, daytime inspections, spot replacement (replacement initiated outside regular inspections), and retroreflectivity deterioration. This is the first model to successfully represent blanket replacement being conducted at a rate of one area per year (which results in balanced workload and cost over time) and the first to quantify the benefits of a grace period.
A set of 24 sign replacement strategies were developed and further studied. The sign replacement strategies were obtained by crossing the different levels of the three control variables: blanket replacement cycles (10, 15, 18, and 20 years), grace period (0, 3, and 5 years), and daytime sign inspections (presence and absence).
The authors found that daytime inspections are an effective way of achieving a low number of unsatisfactory signs while having little effect on cost. Grace period was found to be efficient in reducing costs. In addition, longer replacement cycles (e.g., 20 years) that consider daytime inspections and a grace period resulted in more cost-efficient strategies than those with shorter replacement cycles (e.g., 10 years). This study was based on NC sign data, therefore, its results provide insights into effective practices that could result in more cost-efficient sign replacement strategies.
