The purpose of this research is to assess NCDOT traffic signal maintenance procedures and signal replacement cycle to benchmark their costs so that signal performance is maintained or enhanced and to develop a model for LED powered signal life span. This study answers the question “what is the threshold at which an acceptable working LED traffic signal is in need of replacement?" This study will explore whether or not a systematic signal replacement strategy could be developed and used by any division within NC to enhance performance, reduce waste, reduce cost, and be realistically and efficiently implemented.
We will analyze traffic signal maintenance practices at NC intersections, develop and use statistical and simulation models (validated with actual NCDOT data) to predict future signal replacement needs (based on signal life, cost and field replacement procedures), and estimate budgets based on signal condition, signal replacement rate, and operations costs. These estimates will then be used by NCDOT to improve cost efficiency, manage replacement cycles, and facilitate signal management decisions for maintaining the required level of signal condition and performance.
Currently, NCDOT is using a five year replacement cycle for signal lighting modules. The module consists of a lens, LED, and housing, and costs on the order of $20-$25 each. While the material cost is low, the labor and equipment cost adds significantly to the total cost. But the most important issue lies in safety during replacement. Thus, a longer replacement cycle (lifespan) would not only lower cost, but will increase safety as well.
The essential research questions are the following. (1) What are the visibility requirements of a traffic signal? (2) By using a systematic approach, is it possible to develop an efficient visibility inspection routine? (3) What is the true life span of modern LED signals? (4) What is the optimal signal replacement strategy to lower NCDOT maintenance costs? (5) What is the status of the state wide signal condition? (6) How are signals and lenses currently monitored, tracked, and replaced (RMIP, MMS)?
To answer these questions requires significant interaction with NCDOT personnel in Raleigh and in Division field offices. It also requires a well-founded simulation model that accurately links signal visibility deterioration rate with cost and budgets. We propose to compile, assess, and quantify effectiveness, compliance, and cost savings resulting from this investigation.
The lessons learned from the assessment and analysis will be combined with the experiences of other NC divisions and with knowledge gained from the literature to formulate one or more potential strategies to meet NCDOT needs. In doing so, NCDOT may improve both its overall financial decision making and the management of this critical roadway asset, resulting in overall cost savings and safety enhancement.