Review of U.S. Department of Transportation Truck Size and Weight Study: First Report: Review of Desk Scans (2014)

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10 BRIDGE STRUCTURE The MAP-21 Section 32801 charge to USDOT for the CTSW study contains three references to infrastructure or bridge impacts: Sec. 32801(a)(2): [The study shall:] (2) evaluate the impacts to the infrastructure in each State that allows a vehicle to operate with size and weight limits that are in excess of the Federal law and regulations, or to operate under a Federal exemption or grandfather right, in comparison to vehicles that do not operate in excess of Federal law and regulations (other than vehicles with exemptions or grandfather rights), including— (A) the cost and benefits of the impacts in dollars; (B) the percentage of trucks operating in excess of the Federal size and weight limits; and (C) the ability of each State to recover the cost for the impacts, or the benefits incurred. . . . Sec. 32801(a)(4): [The study shall:] (4) assess the impacts that vehicles that operate with size and weight limits in excess of the Federal law and regulations, or that operate under a Federal exemption or grandfather right, in comparison to vehicles that do not operate in excess of Federal law and regulations (other than vehicles with exemptions or grandfather rights), have on bridges, including the impacts resulting from the number of bridge loadings. . . . Sec. 32801(a)(6)(B): [The study shall estimate:] (B) the effect that any such diversion [from other modes to highways if alternative configurations were allowed to operate] would have on public safety, infrastructure, cost responsibilities, fuel efficiency, freight transportation costs, and the environment. . . .

11 The committee understands that the bridge desk scan was to identify resources pertaining to estimating the consequences of allowing operation of vehicles (including those already in legal operation in certain states or the alternative configurations specified in MAP-21 Section 32801) exceeding present federal size and weight limits that arise from the effect of these vehicles on bridges. Changing size and weight limits changes the loads that individual vehicles impose on bridges and changes the volume and distribution of truck traffic over the road system. Highway agencies may respond by changing practices for design, construction, retrofitting, maintenance, and posting of bridges. The ultimate consequences are changes in highway agency costs to provide highways and in highway user costs and benefits. Is the Desk Scan Thorough? The desk scan covers physical effects of traffic on bridges (deck deterioration and management, fatigue, bridge structure deterioration models, cost allocation methods); owners’ (state and local governments’) bridge management practices that determine how owners would respond to changes in truck characteristics or to observed changes in bridge conditions; highway cost allocation studies of states and other countries, with a focus on bridge costs assigned to trucks in these studies; data sources; and models of how freight mode shift and changes in truck weight limits affect axle load distributions. The desk scan does not include a comparative evaluation of alternative methods of assessing bridge costs of changes in size and weight limits. This omission is especially unfortunate if the conclusion of the committee that conducted the 2002 TRB truck size and weight study (TRB 2002, 3) that “the methods used in past studies have not produced satisfactory estimates of the effect of changes in truck weights on bridge costs” is accepted. The references selected for inclusion in the bibliography appear to be primarily those that are necessary to support a predetermined plan of analysis for the CTSW study. The desk scan does not review the results of past studies of the effects of changes in truck traffic on bridges. Instead, the focus is on methods of analysis and sources of data. One comparison of results

12 that would be especially helpful in the CTSW bridge analysis would be a summary of how past studies have presented the financial impact of changes in size and weight limits on state highway programs over time. Changing limits creates a need for a stream of future capital spending to compensate for the change in useful life of existing bridges and the change in the cost of construction of new bridges. The financial impact would be reported as an increase in resources needed by bridge owners in the next year and in 2 years, 5 years, 10 years, and so forth. The principal risk of changes in limits is that bridge inventories will decay more rapidly than expected without a corresponding increase in funding. The desk scan does not identify resources for carrying out each of the MAP-21 required analyses related to bridges in the CTSW study. Estimates of the costs to the public of the bridge impacts of changes in truck traffic (e.g., costs of traffic disturbance of bridge closings and bridge construction) and assessment of the owners’ abilities to recover their costs are presumably being carried out in other tasks of the CTSW study; methods of conducting such estimates are not discussed in the bridge desk scan (although some of the references cited may contain estimates of these costs). The desk scan does not identify methods or data sources to support estimates of the impacts of changes in limits on bridge barriers, median barriers, or railings. Size and weight limit changes may necessitate changes in safety hardware standards, which would affect the costs of all categories of road construction and reconstruction. On some bridges, the strength of the deck overhang limits the upgrading of safety hardware. Information sources are needed to support estimates of impacts of changes in size and weight limits on design and maintenance of barriers, railings, and other appurtenances, not only on bridges but also on all roads. (Section 7.0 of the safety desk scan cites studies of the compatibility of barriers with vehicles of larger sizes and weights.) The desk scan describes a 2010 truck size and weight study conducted for the District of Columbia Department of Transportation (DCDOT) as (p. 18) “a basis of this study.” The DCDOT study is unpublished, and the absence of a summary of it in the desk scan appears to be a significant omission. The desk scan should cite all major data sources that may be used in the CTSW bridge analysis and describe potential shortcomings of the data. Potential data difficulties include the following:

13  According to the project plan, the CTSW study team will obtain the AASHTOWare Bridge Rating (ABrR) program files from states already using this software. Finding ABrR models of older bridges may be difficult. The pool of available bridge files may be weighted toward bridges with odd configurations, noted deterioration, or some other abnormality.  According to the project plan, costs in the bridge analysis would be from FHWA’s Financial Management Information System (FMIS). However, FMIS is based on project costs. A project may include multiple bridges and elements other than bridges. A method for extracting the bridge-related costs attributable to the change in size and weight limits from the data is required. At least, the desk scan should describe FMIS and cite previous similar applications of the data. The desk scan should identify the National Bridge Inventory database as an alternative or complementary source of cost data.  The bridge analysis relies on WIM data. The desk scan should identify the WIM data to be used and describe the shortcomings of the data for the purposes of the bridge analysis. Is the Desk Scan Missing Literature, Case Studies, Models, or Data That Would Help Achieve the Study Goals? Necessary or potentially useful resources not identified in the desk scan include the following:  The American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) bridge design specifications (AASHTO 2012) would be helpful.  Special Report 225: Truck Weight Limits: Issues and Options (TRB 1990a) and Special Report 227: New Trucks for Greater Productivity and Less Road Wear: An Evaluation of the Turner Proposal (TRB 1990b) provide additional examples of methods and results of estimating the effects of changes

14 in size and weight limits on bridge costs.  Past studies of the implementation of federal Bridge Formula B (e.g., TRB 1990a) may provide useful information.  Studies in the area of structural health monitoring of bridge decks may be useful. Estimates of the effects of limits on deck deterioration should be a major aspect of the CTSW study. The desk scan lacks in-depth review of studies of causes of deck deterioration, deck deterioration modeling, and deck deterioration quantification. The relevance to the CTSW study of some of the references on decks cited in Section 3.3 of the desk scan is unclear.  Coverage of studies related to the service limit state in more depth would be useful [e.g., Evaluation of Serviceability Requirements for Load Rating Prestressed Concrete Bridges (Wood et al. 2007)].  The review of studies of fatigue life is insufficient. A single reference is cited, from Sweden. Most of the studies cited in Section 3.6 of the desk scan appear to focus on fatigue vulnerability and not on the change in fatigue life due to increased truck loads. Potentially useful studies are those of Fisher et al. (1983), Hoadley et al. (1983), Cohen et al. (2003), Reisert and Bowman (2006), and Bowman et al. (2012).  The attention to methods and results of past estimates of shear effects is insufficient. Article 6A.5.8 of the first reference listed in the desk scan, Manual for Bridge Evaluation (2nd edition, 2013), states the following: “The shear capacity of existing reinforced and prestressed concrete bridge members should be evaluated for permit loads. . . .”  The resources cited in Section 3.8.2, Cost Allocation Study Methods and Methodology, appear insufficient for carrying out the determination of load-related cost (except in the case of decks) as described in Section 1.3.2.1 of the bridge project plan.

15 Does the Desk Scan Interpret the Literature Reviewed Correctly? Two interpretations of studies cited in the desk scan would be worth reconsidering. First, the desk scan states (p. 4) that NCHRP Report 575: Legal Truck Loads and AASHTO Legal Loads for Posting “goes to the heart of the Comprehensive Truck Size and Weight Limits Study . . . as it relates to structural impacts on bridges and load postings.” Rating factors are an indication of whether a bridge needs to be posted. The outcome associated with the increased magnitude of stresses related to each alternative vehicle needs to be measured and compared with acceptable stress levels. Degradation is generally associated with the service limit state, as defined in the AASHTO LRFD Bridge Design Specifications (AASHTO 2012). Second, the desk scan appears to indicate (p. 22) that the CTSW study will place little reliance on NCHRP Report 495: Effect of Truck Weight on Bridge Network Costs. The review characterizes it as “a ‘state’ tool,” but apparently the methods therein could be used on any set of bridges, including local and rural bridges. The NCHRP report provides an alternative, stress-based approach to some of the analysis methods proposed in the bridge project plan. The desk scan should include a comparison of these alternatives. Does the Desk Scan Synthesize the Literature and Draw Appropriate Conclusions? The bridge desk scan lacks syntheses of analysis methods or of results of past estimates concerning the effects of changes in size and weight limits. References Abbreviations AASHTO American Association of State Highway and Transportation Officials TRB Transportation Research Board AASHTO. 2012. AASHTO LRFD Bridge Design Specifications, Customary U.S. Units, 6th Edition, with

16 2013 Interim Revisions. Washington, D.C. Bowman, M. D., G. Fu, Y. E. Zhou, R. J. Connor, and A. A. Godbole. 2012. NCHRP Report 721: Fatigue Evaluation of Steel Bridges. Transportation Research Board of the National Academies, Washington, D.C. Cohen, H., G. Fu, W. Dekelbab, and F. Moses. 2003. Predicting Truck Load Spectra Under Weight Limit Changes and Its Application to Steel Bridge Fatigue Assessment. Journal of Bridge Engineering, Vol. 8, No. 5, pp. 312–322. Fisher, J. W., D. R. Mertz, and A. Zhong. 1983. Steel Bridge Members Under Variable Amplitude, Long Life Fatigue Loading. Final report draft. Lehigh University, Bethlehem, Pa. http://preserve.lehigh.edu/engr-civil-environmental-fritz-lab-reports/2246. Hoadley, P., K. Frank, and J. Yura. 1983. Estimation of the Fatigue Life of a Test Bridge from Traffic Data. Research Report 247-4. Center for Transportation Research, University of Texas at Austin. Reisert, J. A., and M. D. Bowman. 2006. Fatigue of Older Bridges in Northern Indiana due to Overweight and Oversized Loads, Volume 1: Bridge and Weigh-in-Motion Measurements. Publication FHWA/IN/JTRP-2005/16-1. Joint Transportation Research Program, Indiana Department of Transportation and Purdue University. TRB. 1990a. Special Report 225: Truck Weight Limits: Issues and Options. National Research Council, Washington, D.C. TRB. 1990b. Special Report 227: New Trucks for Greater Productivity and Less Road Wear: An Evaluation of the Turner Proposal. National Research Council, Washington, D.C. TRB. 2002. Special Report 267: Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles. National Academies, Washington, D.C. Wood, S. L., M. J. Hagenberger, B. E. Heller, and P. J. Wagener. 2007. Evaluation of Serviceability Requirements for Load Rating Prestressed Concrete Bridges. Texas Department of Transportation, Jan.