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1 Background Understanding the costs of highway construction, high- way maintenance, and vehicle operation is essential to sound planning and management of highway investments, especially under increasing infrastructure demands and limited budget- ary resources. While the infrastructure costs borne by road agencies are substantial, the cost borne by the road users are even greater. Therefore, vehicle operating costs (VOCs) should be considered by highway agencies when evaluating pavement investment strategies. For conventional vehicles, these costs are related to fuel and oil consumption, tire wear, repair and maintenance, and depreciation. However, emerging vehicle technologies may involve other cost items. These costs depend on the vehicle class and are influenced by vehicle technology, pavement-surface type, pavement condition, roadway geo- metrics, environment, speed of operation, and other factors. A large body of research is available on the effects of pave- ment condition on vehicle operating costs and on models used to estimate these effects. Much of this information and many of the models were developed on the basis of data gen- erated some 30 years ago in other countries for vehicle fleets that differ substantially from those used currently in the United States and for roadways that differ from those built in the United States. However, information relevant to operat- ing costs of heavy trucks was recently collected in the United States. This information could be used to refine these mod- els or develop models that would better apply to current and future US conditions. Nevertheless, information on the effects of pavement condition on the operating costs of light vehicles (automobiles and pickup trucks) is not readily available. Description of the Problem There are models of vehicle operating costs (and other road user costs) that are a function of road design characteristics, level of congestion, and work zone characteristics. However, unavailability of reliable models for estimating the effects of pavement condition on vehicle operating costs make conduct- ing a comprehensive analysis of highway investment difficult. Therefore, there is a need to develop models applicable to current vehicle technology and to traffic and environmental conditions encountered in the United States. Such models will provide highway agencies with the tools necessary for consid- ering vehicle operating costs in evaluating pavement invest- ment strategies and identifying options that yield economic and other benefits. In this case, benefits include reductions in vehicle operating costs to meet the requirements related to more performance-based analyses of highway needs and jus- tification of expenditures. NCHRP Project 1-45 was initiated to address these needs. Project Objective and Scope The objective of this research was to develop models for estimating the effects of pavement condition on vehicle oper- ating costs. These models were to reflect current vehicle tech- nologies in the United States. The work performed for the research project included the collection and review of relevant literature, current practices, and data information relative to estimating the effects of pave ment condition on vehicle operating costs (i.e., fuel con- sumption, tire wear, and repair and maintenance costs). The research also identified and evaluated current VOC models and recommended models that consider paved surfaces and traf- fic and environmental conditions encountered in the United States and address the full range of vehicle types. However, the research does not include the effects of pavement conditions on changes in travel time, nor does it consider the safety-related, environmental, or other implications of pavement conditions. Research Approach In this study, a large amount of data and information was collected, reviewed, and analyzed to identify the most rele- vant VOC models. This process focused on research that had C h a p t e r 1 Introduction
identified factors affecting vehicle operating costs including pavement conditions. The most relevant reports to this study were those dealing with the relationship between pavement conditions and vehicle operating costs. A detailed investigation involving field surveys to collect pavement condition data and field trials to collect fuel consumption and tire wear data was conducted. These data were used to calibrate and validate fuel and tire wear models and estimate the effects of pavement con- ditions on these VOC components. The research also involved the collection of repair and maintenance data of vehicle fleets from two departments of transportation (Michigan and Texas). The fleet data were used to develop repair and maintenance models. The end products of this research study are improved fuel consumption, tire wear, and repair and maintenance costs models that consider the paved surface conditions encountered in the United States and address the full range of vehicle types. Report Organization The report is divided into seven chapters. Chapter 1 is the introduction. Chapter 2 describes and evaluates existing VOC models. Chapter 3 discusses the calibration and validation of the selected fuel consumption model. Chapter 4 presents the results for the tire wear model. Chapter 5 discusses the development of the repair and maintenance costs model. Chapter 6 investigates the applicability of the improved models to emerging technologies. Chapter 7 summarizes the results of the study including the improved models and model parameters. An attachment to the report presents the user guide for the new VOC models and examples of analy- sis at the project and network levels using the results from this study. Four appendixes to the report are available on the TRB website (http://www.trb.org/Main/Blurbs/166904.aspx). Appendixes A and B present the details of existing fuel and tire consumption models, respectively, and the collected data. Appendix C discusses the details of the repair and main- tenance costs, the data collected from Texas and Michigan Departments of Transportation, and the results of the model development. Appendix D presents a summary of informa- tion on the emerging technologies and their effect on vehicle operating costs. 2