State departments of transportation (DOTs) and other government agencies have invested significant resources in building our nation’s highway system. These investments are embodied in the assets that comprise the network, such as pavements, bridges, lighting, signals, signage, intelligent transportation system (ITS) devices, pavement markings, drainage systems, traffic barriers, landscaping, noise walls, and rest areas. These various assets are expected to provide many years of service, but ultimately may require replacement.
Network preservation activities are the means to ensure realization of the greatest value of past investments in existing assets, ensuring acceptable serviceability for the foreseeable future, until replacement becomes necessary. These activities include both maintenance and rehabilitation.
Preservation activities require resources. These resources are inevitably limited, requiring that DOTs allocate their resources among categories of assets to preserve the network as a whole. The allocation task is complex: for example, various categories of assets perform different functions within the network and comparing their contributions to system serviceability is difficult; funds are sometimes limited to spending on particular asset categories; life expectancies of different categories of assets differ significantly; and the objectives guiding investment may change from time to time, perhaps emphasizing safety or mobility or environmental factors.
Agencies need practical strategies and methods for making preservation-resource allocation decisions. These decisions typically are made within the context of annual budgets within 5- to 6-year capital-budget horizons, but deal with assets that may be expected to have service lives of as much as 50 to 100 years. Agency managers generally seek to optimize asset performance subject to constraints on funds and other resources and must make tradeoffs among several aspects of performance as well as among asset categories and resources.
The objectives of this research were to (a) describe—in practical, usable terms— an analysis framework (including principles, objective functions, and constraints) that may be used to allocate resources across principal categories of highway assets for which a DOT is responsible to ensure system preservation, and (b) demonstrate application of the framework. The research team assessed the decision-making context for preservation-resource allocation within DOTs and the characteristics that a resource allocation strategy must have to be implementable considering such factors as data quality and availability; forecasting tools used in management of various categories of assets, risks and liabilities that agency management must consider, and the changeability of priorities that DOTs experience. Based on their asseessment, the team specified an optimization framework and objective functions useable in preservation-resource allocation.
The team developed a spreadsheet-based approach to implementing the optimization framework and developed examples of its application using data provided by several DOTs. A workshop was held to allow selected practitioners to comment on the optimization approach and help the team to refine specific implementation details to enhance the procedure's utility.
The project report, published as NCHRP Report 736
, documents the project. and presents in detail the proposed procedures for developing and applying the optimization framework to inform an agency's resource allocation decision making. A set of 4 spreadsheet files (in Excel format), functional illustrations of the procedure applyed under scenarios typical of conditions a DOT may face, may be downloaded from the following links: