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25 FRAMEWORK FOR SETTING RESEARCH AND DATA COLLECTION PRIORITIES FHWA asked TRB to include in this interim report a description of the framework that the committee will follow for determining priorities among research and data needs and for defining the roles of USDOT and other participants in its proposed research and data collection plan. Priorities would be a guide to allocating funding and other resources among competing activities and will also be a factor in deciding the sequence of activities in the research program. Defining roles will be an essential part of the research plan because most research and data collection will require active participation of state highway agencies. Some of the research and data needs described above would also require local highway agency and private industry participation. The committee identified the six criteria, defined in the sections below, that it will take into account in its assessment of research priorities. All of the criteria are ways of judging how much the results of a research project would improve the utility of a truck size and weight limit study as a guide for decision makers. The criteria are primarily qualitative, but it may be possible to at least rate each candidate research and data activity on a âhigh-medium-lowâ scale with respect to each of the criteria. Relative Magnitudes of the Potential Cost Changes Caused by a Change in Limits Obviously, improved understanding of potentially large costs from changes in limits is of more importance to decision makers than refined estimates of costs that are likely to be small. Results of past studies indicate that certain categories are likely to predominate decisions. For example, the 1981 and 2000 USDOT studies estimated annualized highway agency bridge-related costs on the order of billions of dollars if gross weight limits were substantially increased (FHWA 1981, II-19; TRB 2002, 61). The 2000 USDOT study estimated highway user costs of traffic congestion caused by bridge work to be greater than the highway agenciesâ construction costs. In contrast, studies have consistently concluded that the change in the cost of pavement construction and maintenance would be relatively small (cost
26 savings on the order of tens of millions of dollars annually) because the changes in limits commonly proposed in the United States do not involve changes in axle weight limits (TRB 2002, 56). Considering these differences, research aimed at better understanding bridge costs is likely to have more value in policy decisions than research on pavement. However, as discussed below, consideration of the criterion of relevance to the regulatory changes under consideration might give higher priority to pavement research. Degree of Uncertainty in Present Estimates A relatively large amount of uncertainty evident in the past estimates of a cost is grounds for assigning priority to the development of improved methods for estimating the cost. Comparing the estimates in the past USDOT and TRB truck size and weight limit studies shows that differences from study to study in the magnitude of impact estimates are greater for certain impact categories than for others. A primary example is estimates of the cost of protecting bridges if gross weight limits are increased. Although the vehicle scenarios in the 2000 and 2016 USDOT studies are not directly comparable, the much smaller bridge cost estimate in the 2016 study is striking. USDOT concluded in the 2016 study that the cost of bridge deck deterioration from changes in limits is unknown (FHWA 2016a, 19). As noted above, the TRB committee that authored TRB Special Report 267 concluded that the basic bridge cost estimation method used in all past studies is invalid (TRB 2002). Likelihood That Research Could Make Progress Some categories of impact may be so inherently difficult to evaluate or model that further research would have a high risk of failing to appreciably reduce uncertainty. The limited resources available for research should be devoted to the projects expected to yield the greatest overall improvement in projections of costs and benefits of changing truck size and weight limits.
27 Public and Interest Group Concerns The authors of past truck size and weight studies recognized the need to give full attention to analysis of the potential impacts of changes in limits that are most visible and of most importance to the public and to interest groups. In making decisions about the regulations, elected officials will require information on the impacts that most concern their constituents. The potential effects of changes in limits on road safety, traffic, and competition between the trucking and railroad industries are impact categories that have received heightened priority because of this consideration. Potential Value of Research Results for General Highway Management Applications Much of the research and data collection activities that USDOT recommended in its 2016 truck size and weight studyâs final report (USDOT 2016, 20â24) would be complex, expensive, and of long duration. Gaining management support and funding for such a research program would probably require showing benefits beyond the narrow application of evaluating changes in federal size and weight regulations. Experience shows that national coordination of existing state and local government data collection programs is especially difficult to achieve. The USDOT recommendations requiring such coordination would be likely to gain support of the agencies whose cooperation would be needed only if they could be shown to have substantial benefits to state and local governments. However, important elements of USDOTâs research needs list could have such broad benefits. For example, research on the determinants of bridge deck performance would have fundamental value for bridge life-cycle cost analysis, design, and asset management. Similarly, expansion of the network of WIM sites could be valuable for a range of asset management and system planning applications. In general, understanding the relationship of traffic characteristics (including truck volume, size, and weight) to highway agency costs (construction, maintenance, and enforcement) and to user costs (safety,
28 congestion, and vehicle wear) is fundamental to highway system management regardless of whether the limits are changed. To earn support for such research and to gain its maximum value, the research must be designed with consideration of the full range of applications. Research with general application will merit high priority. As an alternative to research of broad value, the FHWAâs Office of Freight Management and Operations could sponsor stop-gap research designed solely for its own needs (e.g., to develop a simple model of deck deterioration that would provide a defensible estimate for use in evaluating truck size and weight regulations, but would not be useful for broader bridge engineering applications). Such stop-gap research might merit priority if time, funding, or institutional support for higher-value research was lacking. Assumed Objectives of the Regulatory Changes Under Consideration To set research priorities, it will be necessary to make assumptions about the range of truck size and weight policy options that will require analysis. For example, it was noted above that in past studies, the estimated effect of limit changes on pavement costs has been small because changes in axle weight limits have not been regarded as an important policy option. However, it may be useful for USDOT to have the capability to analyze the consequences of setting axle load limits substantially higher or lower than at present to investigate whether such changes could yield system-level benefits. Although not considered in recent USDOT studies, determination of the optimum axle weight limit was a primary objective of the 1968 USDOT truck size and weight study (Solomon 1972, 1â4). Estimating potential infrastructure savings from more stringent weight enforcement would also require models of the cost of very heavy axle loads. Federal and state truck size and weight regulations have provisions beyond dimensional limits, including route restrictions, equipment requirements, driver qualification requirements, and requirements