NCHRP 08-71 [Final]
Methodology for Estimating Life Expectancies of Highway Assets
| Project Data
||Samuel Labi, Kumares Sinha |
The deterioration of highway infrastructure begins as soon as it is put into service. Effective management of highway system assets requires a good understanding of the life expectancy of each asset. Asset life expectancy is the length of time until the asset must be retired, replaced, or removed from service. Determining when an asset reaches the end of its service life generally entails consideration of the cost and effectiveness of repair and maintenance actions that might be taken to further extend the asset’s life expectancy. Different types of assets, such as pavements, bridges, signs, and signals, will have very different life expectancies. Asset life expectancy also depends on the materials used; demands actually placed on the asset in use; environmental conditions; and maintenance, preservation, and rehabilitation activities performed.
Effective management of highway system assets requires that agency decision makers design and execute programs that maintain or extend the life of the various types of assets in the system at low cost. Designers use estimates of asset life expectancy in their lifecycle cost analysis to make design decisions, but those estimates depend on assumptions about maintenance practices, materials quality, service conditions and characteristics of the asset’s use. If actual service conditions and maintenance activities subsequently differ from the designer’s assumptions, the asset’s life is likely to be different from initial estimates. Better information and tools for estimating asset-life expectancies are needed to guide in-service asset management programs. Research is needed to determine the life expectancies of assets for at least four potential cases: (1) when maintenance and preservation activities are performed as assumed by the designer in the lifecycle cost analysis, (2) when little or no maintenance is performed over the life of the asset, (3) when more aggressive maintenance and preservation activities are performed to extend the asset’s life, and (4) when materials or designs that require no or very little maintenance are used.
The objectives of this research were to (1) develop a methodology for determining the life expectancies of major types of highway system assets for use in lifecycle cost analyses supporting management decision making; (2) demonstrate the methodology’s use for at least three asset classes, including pavement or bridges and two others, such as culverts, signs, or signals; and (3) develop a guidebook and resources for use by state DOTs and others for applying the methodology to develop highway maintenance and preservation programs and assess the impact of such programs on system performance.
The project entailed a review current literature and practices within highway agencies and other industries, such as utilities and vehicle- and equipment-fleet management, to describe the methodologies currently used to determine life expectancy for major assets. The research team considering both new and in-service highway assets such as pavements, bridges, culverts, signs, pavement markings, guardrail, and roadside facilities, describing the factors likely to influence predicted or assumed asset life expectancies. These factors include materials, design criteria, construction quality control, and maintenance policies and practices. Data needs and availability influence analytical ability to estimate and predicting asset life expectancies. Geographic location and highway system management policies also have influence on life expectancies. Considering these several factors, the research team described methodologies for estimating the life expectancy of major types of highway system assets, for use in lifecycle cost analyses supporting maintenance and preservation management decision making.
The research produced a 2-volume report, NCHRP Report 713: Estimating Life Expectancies of Highway Assets. Volume 1 is a guidebook designed to be used by transportation agency staff wishing to estimate asset life expectancies. The second volume documents the research and presents useful background information. These documents (accessible by clicking on the links) are supplemented by a spreadsheet illustrating the computations used for estimating life expectancy of particular assets.