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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"2 Summary of the Roadmap." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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15 2 Summary of the Roadmap The roadmap includes research problem statements outlining 27 research projects in six groups corresponding to the five categories of impact in the Statement of Task and one group of cross­cutting topics (that is, topics relevant to several or all impact categories) (see Table 2­1 at the end of this chapter). The relation of roadmap projects to the structure of a conven­ tional truck size and weight limits study is illustrated in Figure 2­1. PROBLEM STATEMENTS The research problem statements follow a standard outline: 1. Title of the research topic. 2. Problem statement: A summary description of the problem to be solved, together with an explanation of how the problem relates to estimating the costs or benefits of changing truck size and weight limits. 3. Research objective: Specification of the desired research outcome or product (for example, a model, a methodology, a cost estimate). 4. Possible approaches: Outlines of one or more possible research approaches, to indicate the scope of the work and the resources needed. 5. Data requirements: Identification of existing data resources that the research may use and data that would be collected as part of the research.

16 FI G U R E 2 -1 R el at io n of r oa dm ap p ro je ct s to t he s tr uc tu re o f a tr uc k si ze a nd w ei gh t po lic y ev al ua ti on . Ch an ge in pa ve m en t c os ts •  Ho w w ill p av em en t b e af fe ct ed o n al l r oa ds b y ne w a xl e w ei gh t l im its , ax le g ro up in gs , t ire s? (P .1 , P .2 , P .3 , C .4 ) Ch an ge in b rid ge c os ts •  Ho w d o ve hi cl e lo ad s af fe ct b rid ge d et er io ra tio n an d se rv ic e lif e? (B .1 , B .2 , B. 3, B .4 , B .5 , B .6 , C .4 ) •  Ho w sh ou ld lo ad s b e re pr es en te d in d es ig n an d ra tin g? (B .7 ) Ch an ge in sa fe ty c os ts •  Ho w d o siz e an d w ei gh t af fe ct re la tiv e cr as h ris k? (S .1 , S .2 , S .3 , S .4 , S .6 , C .4 ) •  Ho w d o siz e an d w ei gh t af fe ct h an dl in g, st ab ili ty ? Ho w c an p er fo rm an ce b e im pr ov ed ? (S .5 ) M od e an d tr uc k tr af fic v ol um es •  W ha t a re tr uc k tr af fic v ol um es , c on fig ur at io ns , a nd w ei gh t d ist rib ut io ns o n U .S . ro ad s t od ay ? (C .1 ) En fo rc em en t im pa ct •  W ill c ha ng e in li m its af fe ct e nf or ce m en t co st , e ffe ct iv en es s? (E .2 , C .4 ) Tr uc k siz e an d w ei gh t r eg ul at io ns •  Ca n co or di na tio n of si ze a nd w ei gh t l im its w ith ot he r r oa d m an ag em en t p ol ic ie s i m pr ov e sy st em pe rf or m an ce ? (C .2 , C .3 ) Tr uc k siz e an d w ei gh t en fo rc em en t •  W ha t a re m os t e ffe ct iv e en fo rc em en t st ra te gi es , t ec hn ol og ie s? (E .1 , E .3 , E .4 ) O th er c on di tio ns (r eg ul at or y, us er ta x, te ch ni ca l, m ar ke t) Fr ei gh t s hi pp er a nd c ar rie r r es po ns e •  Ho w d o tr uc k op er at in g co st s a nd p er fo rm an ce a ffe ct sh ip pe r a nd ca rr ie r c ho ic es o f f re ig ht m od e an d tr uc k co nf ig ur at io n? (M .1 , M .2 , M .3 ) Sa fe ty Sa fe ty O th er im pa ct s: tr af fic o pe ra tio ns , po llu tio n, e ne rg y, re gi on al , r ai l in du st ry ... Ch an ge in sh ip pe r c os t o f fr ei gh t tr an sp or ta tio n

SUMMARY OF THE ROADMAP 17 6. Present status of research: Literature references to existing research that addresses the problem, to indicate the state of knowledge on the problem and to use as examples of possible research approaches. This also includes references to research on analogous problems that illustrates methods that may be applicable to the problem. 7. Estimated cost and duration of the research. 8. Priority: An assessment of the potential contribution of the research to reducing uncertainty about the likely consequences of changing truck size and weight limits. This assessment also notes potential broader applications of the research results in highway management and planning. The outline is similar to that used for submitting research problems for consideration by the National Cooperative Highway Research Program (NCHRP). For most of the research problems, it was not the intent of the com­ mittee to specify a single acceptable research method. The “Possible Ap­ proaches” section in each research problem statement is intended to clarify the content of the research proposed and to show that the research would be feasible. Investigators undertaking any of the problems would select the method. Selection of the method will depend on the funding available for a project: most problems could be addressed with any of a range of ap­ proaches, from simple methods with relatively low cost but more approxi­ mate results to more data­intensive methods with higher costs but possibly more credible results. Within each impact area (pavement, bridges, safety, enforcement, and mode choice), the division of the research into discrete projects is to some extent arbitrary. The scope of each research problem statement could be conducted as a discrete project that would produce useful results. However, most problem statements also are components of a program or sequence of research projects. Completion of the program would achieve the greatest improvement in evaluations. RESEARCH COST, DURATION, AND SEQUENCING The Statement of Task asks for estimated costs and timelines for the projects in the research roadmap. The cost and duration estimates in each research problem statement represent the judgment of committee members, based on their experience with similar projects. The committee did not carry out detailed cost estimates. In most cases, the cost of a project could vary over a wide range, with a larger budget allowing collection and analysis of a larger dataset.

18 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS An early start would be necessary for research problem statements C.1 (development of truck traffic, weight, and configuration data) and S.1 (enhancement of crash and exposure data for application in a research envi­ ronment), which outline research to develop data required for several other roadmap projects. Within the bridge impacts area, problem statements B.2 and B.3 are for research to develop physical models of the effects of trucks on bridges; these models would then be applied in the research of problem statements B.4 and B.5 to develop methods of estimating life­cycle cost effects of changes in truck sizes and weights. Similarly, in the pavement impacts area, problem statement P.1 is to develop a physical model, and problem statement P.2 would then apply the model in developing a method for estimating life­cycle cost. PRIORITIES The projects in the roadmap are grouped in three priority categories: • Projects included in one of the seven core research tracks defined in the following section: These projects could be started immedi­ ately, have a good probability of producing useful results within a practical time period and budget, and would contribute to the core research program for reducing uncertainty in truck size and weight limit evaluations. • Projects that may be deferred: These projects would be feasible and have value, but are less critical than the projects in the core research tracks for reducing uncertainties in truck size and weight limit evaluations or would be of long duration (for example, projects requiring long­term performance data that are not yet available). • Projects for consideration: These projects would have a relatively high risk of producing inconclusive results, or would be especially expensive and complex. Some of these would have greater prob­ ability of success after successful completion of projects in the first two categories. These projects should be considered in the context of FHWA’s overall research priorities. The category to which a project is assigned does not necessarily reflect the ultimate value of the research if the project could be successfully conducted. CORE RESEARCH TRACKS The committee understands that USDOT has an interest in expeditiously gaining improvements in its ability to evaluate truck size and weight limit policy proposals. At the same time, USDOT may choose to undertake a

SUMMARY OF THE ROADMAP 19 long­term research program to fully meet analysis and information needs for managing the highway freight transportation system. The short­term research program goal would be to provide the capability to respond with the best available impact estimates to the kinds of proposals that arise frequently at the federal and state levels for changes in size and weight regulations. The long­term goal would be to seek major improvements in performance with respect to safety, infrastructure cost, and productivity. Attaining fundamental improvement in USDOT’s capabilities to proj­ ect the effects of changes in truck size and weight regulations will depend largely on improvements in state­maintained data systems, including asset management systems, crash records, and traffic data systems. Improving these systems historically has been a slow process and one outside of direct federal control. Improvements in USDOT capabilities in the short term (for example, in the next 3 to 5 years) will be constrained by the limitations of the existing data systems. Regularly collected data can be supplemented with ad hoc data collection in special studies (as proposed in the problem statements for studies of bridge impacts and comparative crash risk). The applicability of results of special studies to the U.S. road system’s diversity of infrastructure and traffic conditions will remain a source of uncertainty. The committee has defined a core program that could meet the need for improved evaluation capabilities in the short term. The core program is a subset of all the projects in the roadmap that would constitute a practi­ cal package of coordinated research that could be completed within 4 to 6 years for $6 million to $9 million. The intent of the core program would be to provide the greatest reduction in uncertainty achievable within specified time and budget constraints. The research projects would have good prob­ ability of success, and results of most of the projects would have value in applications beyond truck size and weight limit evaluations. The core program includes seven core research tracks. Each track corresponds to one research problem statement or to a series of problem statements. The core research tracks are as follows: • Truck traffic, weight, and configuration database compiled from nationwide weigh­in­motion (WIM) installations and other sources. • Discrete­continuous choice model, or suitable alternative, capable of estimating the effect of changes in truck size and weight regula­ tions and other policies on shippers’ and carriers’ choices of freight mode, vehicle configuration, and shipment size. • Pavement analysis methods for heavier axle limits, multi­axle groupings, and alternative tire and suspension types. • Comprehensive model of the relationship of bridge deterioration and service life to vehicle loads.

20 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS • Comparative evaluations of crash risks of alternative configura­ tions using the case­control method. • Protocols for evaluating the performance of configurations using simulation, track testing, and road trials. • Measurement of relationships between frequency of overloads and enforcement level of effort and methods. The core research tracks would be a reasonable starting point on the ex­ tensive program of research in the full roadmap. Exclusion of a project from the core is not meant to imply that the project necessarily would be of less value or less feasible than the projects included. Selection of the first projects in a future research program will be a USDOT decision that will depend on department­wide research priorities and analysis needs. The seven core research tracks are described below (with reference to the detailed definitions in the research problem statements) and summarized in Table 2­2 at the end of this chapter. Truck Traffic, Weight, and Configuration Database from Nationwide WIM Data and Other Sources (Problem Statement C.1) Using the WIM and vehicle classification data that are now collected by the states and compiled by FHWA, this research would develop procedures for data editing and quality control and methods for appropriate weighting of observations to produce a credible base­year estimate of truck traffic vol­ umes and weight spectra for the U.S. road system. The research would also provide the truck weight data needed for infrastructure impact modeling research projects in the roadmap. Baseline estimates of traffic volumes and axle­weight, gross­weight, and configuration­type distributions are necessary in estimating infrastructure cost, safety, freight cost, and mode share impacts of changes in truck size limits and developing models of the relation of loads to bridge and pave­ ment costs. More reliable truck weight and configuration data could be produced by establishing a network of WIM installations designed according to scien­ tific sampling principles to meet the requirements of the intended research and management applications; however, creation of such a network would be a long­term project. Model of Mode and Vehicle Choice (Problem Statements M.1 and M.2) The research would develop a model for projecting the effect of changing size and weight limits on distribution of freight among modes (truck, rail,

SUMMARY OF THE ROADMAP 21 and possibly barge) and the distribution of truck freight among truck types. The model would be of the discrete­continuous choice type, or a suitable alternative, estimated econometrically from observations of shipper or car­ rier mode and vehicle choice decisions for individual shipments. The costs and benefits of a change in size and weight limits will be driven by the effect of the change on the volume of truck freight traffic and on the distribution of truck types that carry the freight. If all costs and ben­ efits were simply proportional to the volume of freight in the new vehicles, the magnitude of freight shifts might not be critical to regulatory decisions. However, the relationship depends on the impact category. For example, bridge costs, as conventionally estimated, are insensitive to the volume of traffic diverted to new vehicles. Safety and pavement costs of a limit change that allows higher­capacity trucks are sensitive to the net effect on truck traffic volume of higher capacity per truck and the new freight attracted to the roads by lower costs. In addition, a freight market model is required to evaluate the effect of coordinating truck user fees with size and weight limits. The TRB committee that reviewed the technical analyses of the USDOT 2016 truck size and weight study identified shortcomings in the model FHWA now uses for projecting mode choice and concluded that a new method is needed (TRB 2015, 38–42). The present model is deterministic rather than stochastic; this structure tends to exaggerate the sensitivity of mode choice to changes in relative costs of modes (Abate et al. 2018). The method of the USDOT 2016 study uses averages derived from aggregate data in place of actual individual shipment characteristics as model inputs; this method does not yield credible projections (TRB 2015, 39–40). Research nearing completion in the National Cooperative Freight Re­ search Program (NCFRP) is expected to provide a suite of practical discrete­ continuous choice models of mode choice (between truck and rail), by commodity, applicable to truck size and weight limit evaluations. Because of limitations in the available freight shipment data, the NCFRP models cannot be used to estimate how changes in the regulations would affect choices among truck configurations. Development of the vehicle choice component of the choice model would require new data collection. The choice model would not replace all the components of the freight market impacts evaluation in the USDOT 2016 study; other models would be needed to project rail revenue impact and the route distribution of truck traffic.

22 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS Pavement Analysis Methods for Heavier Axle Limits, Multi-Axle Groupings, and Alternative Tire and Suspension Types (Problem Statement P.1) This research would develop a pavement analysis framework that real­ istically simulates the impact of vehicles with maximum axle and gross weights, axle configurations, and lengths that differ from those in common use today on the actual pavements of the U.S. road system. Pavement costs have not been a major source of uncertainty in past truck size and weight studies because the majority of regulatory alternatives evaluated did not involve changes in axle weight limits. If maximum axle weights remain unchanged, pavement cost changes will be modest, and ex­ isting models are adequate to project the effects. However, USDOT should have the capability to evaluate changes in axle weight limits, because it is unlikely that the present limits are optimum for economic highway opera­ tion in the long term. Existing pavement models are unreliable for project­ ing the effects of maximum axle weight substantially different from the present or multi­axle groupings and spacings that differ from present use. Enhanced pavement models are also needed to evaluate opportunities to reduce pavement wear through tire configuration and advanced suspen­ sion designs and through control of vehicle spacing and tracking (wander) in truck platoons in future automated and connected operations. Comprehensive Model of the Relationship of Bridge Deterioration and Service Life to Vehicle Loads (Problem Statements B.2 and B.3) This research would assemble historical truck traffic and bridge condition data for a sample of bridges to validate or calibrate engineering models of the relationship of loads to rate of deterioration and to estimate statistical relationships between loads and deterioration. Past USDOT and TRB stud­ ies estimated that costs to correct structurally inadequate bridges would be the largest estimated cost of allowing substantially higher gross weight limits. However, the TRB Commercial Motor Vehicles committee (TRB 2002, 63–69) concluded that the method of estimating the effect of changes in truck weights on bridge costs in most past studies is logically flawed and has not produced life­cycle cost estimates useful for guiding decisions. Improved estimates require a model to link bridge deterioration and loss of service life to vehicle loads. The research would use existing historical truck weight and bridge con­ dition data. As an alternative, condition data would be collected specially for the research. The research could include use of new methods for im­ proving the efficiency of bridge condition data collection, for example, lidar (light detection and ranging) technology. If a large database of historical

SUMMARY OF THE ROADMAP 23 bridge condition and truck traffic data is created, machine learning may be applicable to identify relationships of bridge condition and condition trend to bridge characteristics and truck load history. FHWA’s Long­Term Bridge Performance Study could produce data better suited for modeling the effect of truck traffic on bridge performance. Comparative Evaluations of Crash Risks by the Case-Control Method (Problem Statements S.1 and S.3) This research would develop and demonstrate procedures for measuring relative crash risks of alternative truck types using the case­control study design, for application in evaluations of proposed changes in truck size and weight limits. A case­control study of the relative crash risk of alternative truck types monitors occurrences of truck crashes on a road system and subsequently, at the site of each crash and typically at the same time of day and on the same day of the week, collects data on the characteristics of all trucks in the traffic stream. Comparing trucks in crashes (the cases) to trucks in the traffic stream (the controls) reveals characteristics that are over­ or underrepresented among the crash­involved trucks. The case­control method has less demanding data requirements than the alternative method of directly measuring crash involvement rates from systemwide crash records and estimates of vehicle miles of travel by truck type over a road system. The method produces estimates of relative risks rather than crash rates. Some critical variables that influence risks (for ex­ ample, driver characteristics) can only be obtained if control vehicles are stopped and inspected. The method can only be applied to compare truck types that are in general use on the road system or that are taking part in a road trial. Case­control studies are the method most likely to succeed in the short term in improving quantitative understanding of the relationship of truck configuration and weight to crash risk. The method has been demonstrated in studies by the Insurance Institute for Highway Safety (Braver et al. 1997; Stein and Jones 1988; Teoh et al. 2017). In the long term, improvements in traffic monitoring and in crash record systems will support useful direct measurements of crash rates. Protocols for Evaluating Performance of Configurations with Simulation, Track Testing, and Road Trials (Problem Statements S.5 and C.4) A research program to develop protocols for the use of vehicle performance simulation modeling, track testing, and trials in evaluations of truck size and weight limits would define performance measures; identify appro­ priate models; define test procedures; determine the scale, participation

24 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS requirements, and data collection and analysis methods of trials; design an administrative structure; and finally conduct selected evaluations as a demonstration of the procedures. Predictions made in past truck size and weight limit studies of the safety consequences of changing the limits have most commonly relied on com­ parative crash rate estimates derived from historical data. However, changes in federal limits are likely to lead to use of new vehicles with little record of previous use. Computer simulation modeling of vehicle dynamic behavior and measurement of vehicle performance on a test track are means of com­ paring alternative vehicles with respect to performance characteristics that are believed to be linked to crash risk (for example, performance during braking, off­tracking in turns, and behavior during sudden steering ma­ neuvers). Vehicle dynamic behavior is also linked to pavement and bridge impacts. Simulation and testing can guide performance­based regulations that require trucks to meet minimum standards with respect to handling, stability, and infrastructure interaction. Some past U.S. truck size and weight studies have included vehicle performance simulation modeling and track testing, but the results have seldom been central to the studies’ conclusions and recommendations. Sophisticated simulation models are available for this purpose, and regu­ latory programs in other countries (including Canada [Woodrooffe et al. 2010] and Australia [NTC 2008]) provide examples of the application of such evaluations. Road trials would be a final evaluation stage following simulation and track testing. A trial would evaluate performance of a new configuration in commercial use on a limited scale and under controlled conditions. Relationship Between Frequency of Overloads and Enforcement Methods and Level of Effort (Problem Statement E.1) This research would determine the relationship between the frequency of overloads on states’ highways and characteristics of the states’ truck weight enforcement programs, including level of effort, methods, and legal provisions. Enforcement effectiveness would be measured from weight data developed in the first core research track above. Results would be applicable for assessing the impact of a change in size and weight regulations on enforcement cost and effectiveness and for coordinating size and weight regulations with enforcement practices. The results also would allow truck size and weight enforcement agencies to more accurately predict the outcomes of resource investments and guide im­ provements in the cost­effectiveness of enforcement, regardless of whether size and weight limits are changed.

SUMMARY OF THE ROADMAP 25 TABLE 2-1 Problem Statement Topics in the Research Roadmap Key Priority: • Projects included in one of the seven core research tracks: These projects could be started immediately, have a good probability of producing useful results within a practical time period and budget, and would contribute to the core research program for reducing uncertainty in truck size and weight limit evaluations. Most also would have broader value (beyond truck size and weight limit evaluations). • Project that may be deferred: These projects would be feasible and would have value, but are less critical for reducing uncertainties in truck size and weight limit evaluations or would be of long duration (e.g., projects requiring long­term performance data that are not yet available). • Projects for consideration: These projects would have a relatively high risk of producing inconclusive results or would be especially expensive and complex. FHWA should consider the research in the context of its overall research priorities. Broader Applications: Value of the research for applications in highway management and planning, beyond evaluation of changes in truck size and weight limits. Coordination Requirements: Certain projects would be most practically conducted in conjunction with related research by USDOT or state agencies. Project Priority Broader Applications Coordination Requirements Pavement Research P.1 Realistic assessment of impact of a change in truck size and weight limits on the condition of pavements of the road network Core track project Identify opportunities to control pavement costs through modification of axle configurations, tires, suspensions P.2 Method of estimating the effects of a change in truck size and weight limits on highway agency pavement costs and highway user costs May be deferred P.3 Effect of truck platooning on pavement performance and costs and methods to control the effect May be deferred Identify opportunities to mitigate pavement cost through adjustments to spacing or tracking in platoons Truck component manufacturers, truck operators continued

26 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS Project Priority Broader Applications Coordination Requirements Bridge Research B.1 Compilation of information from highway agencies on costs and decision criteria for bridge repair, rehab, strengthening, and replacement For consid­ eration Provide bench­ mark for agency bridge manage­ ment practices State and local highway agencies B.2 Model of effect of wheel loads on bridge deck deterioration and service life, supported by field performance data Core track project Aid bridge management and deck design State and local highway agencies B.3 Models of effect of changes in size and weight on common bridge types, including effect on service life of load­carrying members Core track project Aid general highway agency bridge management State and local highway agencies B.4 Method for estimating effect of changes in size and weight limits on life­cycle costs of bridge decks May be deferred B.5 Method for estimating the effect on bridge life­cycle cost of the change in deterioration and service life caused by changes in size and weight limits May be deferred B.6 Development of a replacement for the “Formula B” provision in federal law that more appropriately controls weights of short, heavy vehicles May be deferred B.7 Development of a revised deck design load and permit design load and calibration of load factors for both May be deferred Provide revised design loads to accommodate present actual loads Safety Research S.1 Enhancement of crash and exposure data for application in a research environment Core track project State and local highway and highway safety agencies S.2 Route­based or network­based comparative evaluations of safety performance of truck configurations For consid­ eration State and local highway and highway safety agencies; NHTSA TABLE 2-1 Continued

SUMMARY OF THE ROADMAP 27 Project Priority Broader Applications Coordination Requirements S.3 Comparative evaluations of safety performance of truck configurations using the case­control method Core track project State and local highway, highway safety, enforcement agencies S.4 Comparative evaluation of safety performance of truck configurations using trucking company data For consid­ eration State and local highway, enforcement agencies; truck operators S.5 Evaluation of safety performance of truck configurations with computer simulation modeling and track testing Core track project Identify safety improvement op­ portunities within present limits S.6 Model to project frequency of crashes on a road as a function of vehicle mix and traffic volume on the road May be deferred Evaluate safety policies concerning enforcement, traffic management, and road design Enforcement Research E.1 Relationship between enforcement effort and compliance with size and weight laws Core track project Aid planning and budgeting enforcement programs State and local highway, highway safety, enforcement agencies E.2 Detailed accounting of truck size and weight enforcement costs For consid­ eration Provide a bench­ mark for costs and expenditures Enforcement agencies E.3 Survey of truck size and weight enforcement and regulation in other countries May be deferred Identify immediately applicable improvements Road authorities of other countries E.4 Pilot studies to evaluate alternative enforcement methods, including information technology applications and automated enforcement May be deferred Identify immediately applicable improvements State and local highway and enforcement agencies; technology developers TABLE 2-1 Continued continued

28 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS Project Priority Broader Applications Coordination Requirements Mode and Vehicle Choice and Freight Market Research M.1 Adaptation and testing of freight mode choice models for application in truck size and weight limit policy studies Core track project M.2 Mode and vehicle choice model for application in truck size and weight limit policy studies Core track project Evaluate user fee changes and other policies to mitigate truck costs May require shipper or truck operator survey; Census Bureau M.3 Method of projecting railroad industry revenue impact of changes in size and weight limits, including short line impacts For consid­ eration Railroad companies, FRA, Surface Transportation Board Cross-Cutting Topics; Evaluation of Regulatory Options C.1 Truck traffic, weight, and configuration databases necessary for truck size and weight research and evaluations Core track project Aid freight planning and asset management State and local highway agencies, FHWA Long­Term Infrastructure Programs C.2 Methods for incorporating common features of regulatory schemes in evaluations of costs and benefits of changing truck size and weight limits May be deferred C.3 Analysis framework for evaluating the potential of the coordination of size and weight regulations with other road management policies May be deferred Evaluate coordination benefits under present size and weight limits C.4 Protocols for staged pilot evaluations of truck configurations Core track project State and local highway agencies, highway safety agencies, enforcement agencies; truck operators TABLE 2-1 Continued

29 T A B L E 2 -2 C or e R es ea rc h T ra ck s Pr oj ec t D es cr ip ti on Im po rt an ce f or E va lu at in g L im it s Sh or tc om in gs o f E xi st in g M et ho ds Fe as ib ili ty D ur at io n; C os t Fr ei gh t M ar ke t an d T ra ffi c T ru ck t ra ffi c, w ei gh t, an d co nfi gu ra ti on da ta ba se f ro m W IM an d ot he r so ur ce s E st im at e tr af fic v ol um es an d w ei gh t sp ec tr a fo r U .S . ro ad s ys te m ; pr ov id e w ei gh t da ta f or im pa ct m od el in g N ec es sa ry f or e st im at es of a ll im pa ct s of ch an ge s in l im it s an d fo r de ve lo pi ng b ri dg e an d pa ve m en t m od el s St an da rd d at ab as e of tr af fic v ol um es a nd w ei gh t sp ec tr a do es n ot ex is t FH W A V eh ic le T ra ve l In fo rm at io n Sy st em , U SD O T C om pr eh en si ve T ru ck S iz e an d W ei gh t L im it s St ud y pr ov id e st ar ti ng p oi nt 14 –2 2 m on th s $6 00 ,0 00 – $8 50 ,0 00 E ar ly co m pl et io n w ou ld f ac ili ta te in fr as tr uc tu re , en fo rc em en t re se ar ch D is cr et e- co nt in uo us ch oi ce m od el o f fr ei gh t m od e an d ve hi cl e co nfi gu ra ti on c ho ic e D ev el op m od el f or pr oj ec ti ng e ff ec t of ch an ge s in t ru ck c os ts on f re ig ht m od e sh ar e an d co nfi gu ra ti on c ho ic e Im pa ct s of a c ha ng e in l im it s ar e dr iv en by t he e ff ec t on t ru ck fr ei gh t tr af fic a nd co nfi gu ra ti on s us ed M et ho d of U SD O T 20 16 s tu dy d ep en ds o n ar bi tr ar y as su m pt io ns ; de te rm in is ti c m od el s ov er st at e m od e sh if t C ur re nt N at io na l C oo pe ra ti ve F re ig ht R es ea rc h Pr og ra m pr oj ec t de ve lo pi ng m od e ch oi ce m od el ; ve hi cl e ch oi ce m od el m ay r eq ui re n ew d at a co lle ct io n 30 –3 6 m on th s $1 ,2 50 ,0 00 – $1 ,5 50 ,0 00 In fr as tr uc tu re Pa ve m en t an al ys is m et ho ds f or h ea vi er ax le li m it s an d ac ti ve su sp en si on s ys te m s D ev el op m et ho d to si m ul at e im pa ct o f hi gh er m ax im um a xl e w ei gh ts a nd d iv er se a xl e co nfi gu ra ti on s U SD O T r eq ui re s th e ca pa bi lit y to e va lu at e ch an ge s in a xl e w ei gh t lim it s an d di ve rs e m ul ti ­ ax le g ro up s Pr es en t m od el s ar e un re lia bl e fo r he av y ax le s, m ul ti ­a xl e gr ou ps , an d ov er la y pa ve m en ts R ec en t re se ar ch o n co st s of h ea vy p er m it v eh ic le s su gg es ts d ir ec ti on s fo r m od el d ev el op m en t 30 –3 6 m on th s $8 50 ,0 00 – $1 ,0 00 ,0 00 co nt in ue d

30 Pr oj ec t D es cr ip ti on Im po rt an ce f or E va lu at in g L im it s Sh or tc om in gs o f E xi st in g M et ho ds Fe as ib ili ty D ur at io n; C os t C om pr eh en si ve m od el of t he r el at io ns hi p of br id ge d et er io ra ti on a nd se rv ic e lif e to v eh ic le lo ad s E st im at e re la ti on sh ip o f lo ad s to d et er io ra ti on an d lo ss o f se rv ic e lif e us in g br id ge c on di ti on an d tr af fic d at a C os ts r el at ed t o st ru ct ur al i na de qu ac y ar e po te nt ia lly a m aj or co st o f so m e lim it ch an ge s Pa st m et ho ds a re n ot ca pa bl e of p ro je ct in g ph ys ic al e ff ec ts o n br id ge c on di ti on o f ch an ge s in l im it s Si m pl e m od el c ou ld b e de ve lo pe d w it h av ai la bl e lo ad a nd b ri dg e co nd it io n da ta 28 –3 6 m on th s $1 ,0 50 ,0 00 – $1 ,6 50 ,0 00 Sa fe ty E va lu at io ns o f re la ti ve cr as h ri sk s of a lt er na ti ve tr uc k ty pe s by t he c as e- co nt ro l m et ho d D ev el op a nd d em on ­ st ra te p ro ce du re s fo r m ea su ri ng r el at iv e cr as h ri sk s of a lt er na ti ve t ru ck ty pe s us in g th e ca se ­ co nt ro l st ud y de si gn A n es ti m at e of t he re la ti ve c ra sh r is k of al te rn at iv e tr uc k ty pe s is ne ce ss ar y fo r pr oj ec ti ng sa fe ty i m pa ct o f lim it ch an ge s D at a lim it at io ns h av e hi nd er ed a tt em pt s at di re ct m ea su re m en t of cr as h ra te s of a lt er na ti ve ve hi cl es T ru ck c ra sh s tu di es b y In su ra nc e In st it ut e fo r H ig hw ay S af et y sh ow fe as ib ili ty 30 –4 8 m on th s $8 50 ,0 00 – $1 ,4 00 ,0 00 Pr ot oc ol s fo r ev al ua ti ng tr uc k pe rf or m an ce w it h si m ul at io n, t ra ck t es ti ng , an d fie ld t ri al s D ev el op p ro to co ls fo r us e of s im ul at io n m od el in g, t ra ck t es ti ng , an d tr ia ls i n ev al ua ti on s of l im it s W ou ld p ro vi de m ea ns t o co m pa re v eh ic le s’ p er ­ fo rm an ce c ha ra ct er is ti cs lin ke d to c ra sh r is k; c an gu id e pe rf or m an ce ­b as ed re gu la ti on C ha ng es in li m it s m ay le ad t o us e of n ew ve hi cl es f or w hi ch s af et y ca nn ot b e ev al ua te d w it h hi st or ic al d at a E xp er ie nc e in p as t U .S . st ud ie s, u se i n ot he r co un tr ie s in di ca te pr ac ti ca lit y 30 –3 6 m on th s $1 ,5 00 ,0 00 – $3 ,7 00 ,0 00 E nf or ce m en t R el at io ns hi ps b et w ee n en fo rc em en t le ve l o f ef fo rt a nd f re qu en cy o f vi ol at io ns o f si ze a nd w ei gh t re gu la ti on s D et er m in e re la ti on sh ip s be tw ee n ov er lo ad fr eq ue nc y an d ch ar ac te ri st ic s of w ei gh t en fo rc em en t pr og ra m s: le ve l of e ff or t, m et ho ds , le ga l pr ov is io ns A pp lic ab le f or a ss es si ng im pa ct o f a ch an ge i n lim it s on e nf or ce m en t, co or di na ti ng r eg ul at io ns w it h en fo rc em en t, im pr ov in g en fo rc em en t co st ­e ff ec ti ve ne ss T he c om bi ne d ef fe ct of s iz e & w ei gh t lim it s an d en fo rc em en t in de te rm in in g ac tu al a xl e w ei gh ts h as n ot b ee n an al yz ed i n pa st t ru ck si ze a nd w ei gh t st ud ie s W ou ld d ep en d on tr uc k w ei gh t da ta ba se fr om a p ri or r oa dm ap pr oj ec t; w ou ld r eq ui re da ta c ol le ct io n on en fo rc em en t ef fo rt a nd pr ac ti ce s 18 –2 4 m on th s $5 00 ,0 00 – $7 50 ,0 00 (a ss um in g w ei gh t da ta a re av ai la bl e fr om a pr io r pr oj ec t) T A B L E 2 -2 C on ti nu ed

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TRB's Truck Size and Weight Limits Research Plan Committee has issued its second and final report, Research to Support Evaluation of Truck Size and Weight Regulations, to the U.S. Department of Transportation. The report presents a research plan to reduce the major sources of uncertainty in projections of the consequences of proposed changes in truck size and weight limits. The report defines a program of 27 coordinated research projects in six areas.

The committee acknowledges that improvements in models for projecting impacts of changes in truck size and weight limits, while necessary, will not guarantee the success of future truck size and weight policy studies. Future studies will be useful as guides for decisions only if policy objectives and practical policy options are clearly defined, the analysis is logically structured to reveal the most promising policies, and uncertainties are properly characterized.

The committee issued its first report in April 2018, which summarized the research recommendations of past truck size and weight limit studies and identified criteria for deciding the priority of topics for inclusion in the research plan.

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