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1 Introduction The Interstate Highway System is not only a testament to Americaâs engineering prowess but also an embodiment of what the country can accomplish when its leaders are united behind a common vision. It is perhaps not surprising that the generation that waged World War II would conceive of, plan, and build the Interstates. The president who led the countryâs war effortâFranklin D. Roosevelt (see Figure 1-1)âsketched the trunk Interstate routes on a map of the continental United States (Edwards 2018). One of his top generals during the warâDwight D. Eisenhower (see Figure 1-1)âwould later sign into law a dedicated fuel tax as the means to pay for the systemâs construction. The soldiers and sailors who returned from the war would have a lead role in designing, engineering, building, and administering this nascent system. Before President Eisenhower signed the Federal-Aid Highway Act of 1956, which authorized and created a funding mechanism for the Dwight D. Eisenhower National System of Interstate and Defense Highways, the countryâs interstate and interregional highway network consisted of a loosely integrated collection of state and U.S. routes. While it included some modern freeways with divided lanes and access control, often on tolled turnpikes, the collection lacked the interconnectivity and standardized design that would set the new Interstate Highway System apart. At the dawn of the Interstate System, long-distance travel often meant driving on routes interrupted by traffic lights; passing through town centers; and traversing roads of widely varying quality, signage, and configuration (TRB 2016, 45). Even shorter trips between neighboring cities could be slow and meandering. Today, the 11
12 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM ability to drive hundreds of miles on the same route through multiple states without crossing a single intersection is taken for granted. In the transportation domain, the United States has arguably never accomplished more than it did during the Interstate era. The system has become vital to the nationâs economy and central to the daily lives of many millions of Americans. Today, it accounts for one-quarter of the countryâs vehicle-miles traveled (VMT), including more than half of all long-haul truck VMTâeven though it accounts for just slightly more than 1 percent of public road mileage (FHWA 2017a). With a layout that closely resembles the network envisioned by Presidents Roosevelt and Eisenhower, the sys- tem serves more trafficâmore than 800 billion VMT annually (FHWA 2017b)âthan was traveled on the entire U.S. road network in 1956 when the Interstate System was launched (FHWA 2014). Much of the Interstate System, however, is now more than 50 years old and is showing its age from the stress of heavy and largely unanticipated levels of use. While the systemâs scope of coverage, or route footprint, has FIGURE 1-1 President Franklin Roosevelt and General Dwight Eisenhower in 1943. SOURCE: National Archives.
INTRODUCTION 13 largely remained the same throughout this period, the U.S. population and economy have undergone major changes, including marked growth in parts of the country that were lightly populated in 1956. Such locales retain a density of Interstate routes today that is modest relative to their current and forecast populations. Originally designed to serve cities by connecting them to one another, the urban portions of the system have transformed metropolitan regions by becoming primary corridors for commuting and other local travel, accommodating traffic volumes not imagined when the routes were initially planned. As the owners and operators of the Interstate Highway System, states have regularly undertaken its maintenance and repair and periodically re- constructed portions of the system. Nonetheless, they have been severely challenged to keep the systemâs assets in satisfactory condition and its operations and capacity aligned with the growth and changes in traffic demand. Original traffic projections by many states and metropolitan re- gions grossly underestimated the popularity of the Interstate System not only for local commuting but also for the transport of freight. Increas- ingly heavier trucks using the system in higher volumes have added to the systemâs punishment and have led to a mismatch between the conditions for which the highways were designed and the conditions they have faced. On many highway segments, pavement bases and subbases date back to the original Interstate construction phase or before, necessitating more frequentâand often complex and costlyâmaintenance and repair work on heavily trafficked, high-demand routes. Moreover, while many bridges in southern and western states have thus far remained serviceable beyond their 50-year design lives without major repair work, many bridges in northern and midwestern states that have sustained severe weather and high traffic loadings have required frequent redecking. Aging bridges across the system, including a growing share that have exceeded their design lives, will require major repair, rehabilitation, and replacement, an inevitability that cannot be forestalled much longer. Fortunately, as it enters its seventh decade of service, the Interstate System is reaping, or set to reap, the benefits of dramatic, unforeseen technological changes. Advances in materials, construction methods, elec- tronics, communications, and other areas are providing new capabilities and opportunities to increase and manage traffic capacity; reduce system congestion and environmental impacts; increase system safety; and reduce the cost of highway maintenance, repair, and reconstruction. However, owners of the system are also facing other unforeseen developments, nota- bly the need to reduce the systemâs vulnerability and increase its resilience to the effects of climate change. And as highly instrumented vehicles and highways become commonplace, a new challenge will be confronted in the field of cybersecurity.
14 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM In the context of the historical pattern of underestimating traffic load- ings, together with the unanticipated requirements for the system to be made resilient to future climate change and capable of accommodating an increasingly automated vehicle fleet with concomitant cyber threats, the In- terstate Highway System and its upkeep must be viewed through the lens of an ever-changing demographic, economic, environmental, and technologi- cal landscape. To keep pace with these changes, the system cannot simply be preserved and restored; rather, planning and reinvestment choices must be made with an emphasis on renewal, modernization, and adaptability. The latter emphasis is particularly critical because the expected useful life of most highway elements far exceeds the ability to foresee the relatively distant future (say, beyond 20 years). STUDY CHARGE In December 2015, the Fixing Americaâs Surface Transportation (FAST) Act was signed into law. Section 6021 of the law provides for the National Academies of Sciences, Engineering, and Medicine, under the auspices of the Transportation Research Board (TRB), to âconduct a study on the ac- tions needed to upgrade and restore the Dwight D. Eisenhower National System of Interstate and Defense Highways to its role as a premier system that meets the growing and shifting demands of the 21st century.â The full study charge, as it appears in the law, is shown in Box 1-1; also shown is an additional task requested by the Federal Highway Administration (FHWA), which provided funding for the study. In essence, TRB was asked to convene a special study committee to consider â¢ Future demands on the Interstate Highway System, including com- mercial and passenger traffic flows to serve future economic activ- ity and growth; â¢ The expected condition of the system over the next 50 years, in- cluding long-term deterioration and reconstruction needs; â¢ Technological capabilities that will enable the application of mod- ern standards of construction, maintenance, and operations and the furthering of safety and system management; â¢ Highway routes that should be added to the system to serve na- tional traffic flows more efficiently; â¢ The resources necessary to restore and upgrade the system to meet the growing and shifting demands of the 21st century; and â¢ How the system can provide more access to such opportunities as employment and education, and have positive impacts on commu- nities and quality of life.
INTRODUCTION 15 In the FAST Act, Congress encouraged the study committee to consult with FHWA and state departments of transportation (DOTs), metropolitan and local transportation planning agencies, the motor carrier and freight shipping industries; other operators and users of Interstate highways; high- way safety advocates; and other interests, as deemed appropriate by the committee. The committee was further advised to employ and build on the meth- odology for estimating Interstate investment needs proposed in the report of National Cooperative Highway Research Program (NCHRP) Project 20-24(79), Specifications for a National Study of the Future 3R, 4R, and Capacity Needs of the Interstate System (Miller et al. 2013). This methodol- ogy, which is discussed in greater detail later in the present and subsequent chapters of this report, involves the application of FHWAâs long-standing modeling systems for highway and bridge investment needs, coupled with case studies of Interstate construction and reconstruction projects. As de- scribed in the NCHRP report, the purpose of the methodology is to relate current Interstate System condition and performance levels to future levels that will be necessitated by changes in system use, and to estimate the in- vestments required to achieve the needed condition and performance levels. Drawing on its membersâ experience and expertise, informed by consul- tations with outside parties and methods for estimating investment needs, the study committee was asked by Congress to make recommendations âregarding the features, standards, capacity needs, application of technolo- gies, and intergovernmental roles to upgrade the Interstate System.â The committee was further asked to indicate any revisions to law that may be needed to further any recommended actions, as well as to identify the required resources. STUDY APPROACH As detailed in Box 1-1, the multifaceted charge for this study delineates a series of issues to be addressed (e.g., future demands on the system and levels of investment needed to meet those demands), offers instructions and advice on the conduct of the study (e.g., consulting with outside parties and using particular methodologies for estimating investment needs), and identifies candidate topics for recommended action (e.g., system features, standards, capacity needs, application of technologies, intergovernmental roles). The charge is also clear in inviting the study committee to advise on any changes in law that may be needed to further the recommended ac- tionsâpresumably to include any changes that may be needed to authorize and appropriate future investments in the Interstate Highway System. To fulfill this charge, the National Academies appointed a committee whose members brought to bear a wide and varied range of perspectives,
16 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM BOX 1-1 Section 6021 FAST ACT, Request for This Study The Secretary shall enter into an agreement with the Transportation Research Board of the National Academies of Sciences, Engineering, and Medicine to conduct a study on the actions needed to upgrade and restore the Dwight D. Eisenhower National System of Interstate and Defense Highways to its role as a premier system that meets the growing and shifting demands of the 21st century. In conducting the study, the Transportation Research Board shall build on the methodologies examined and recommended in the report prepared for the American Association of State Highway and Transportation Officials titled National Cooperative Highway Research Program Project 20-24(79): Specifications for a National Study of the Future 3R, 4R, and Capacity Needs of the Interstate System, dated December 2013. The studyâ(1) shall include specific recommendations regarding the fea- tures, standards, capacity needs, application of technologies, and intergovern- mental roles to upgrade the Interstate System, including any revisions to law (including regulations) that the Transportation Research Board determines ap- propriate; and (2) is encouraged to build on the institutional knowledge in the highway industry in applying the techniques involved in implementing the study. In carrying out the study, the Transportation Research Board shall determine the need for reconstruction and improvement of the Interstate System by consid- eringâ(1) future demands on transportation infrastructure determined for national planning purposes, including commercial and private traffic flows to serve future economic activity and growth; (2) the expected condition of the current Interstate System over the period of 50 years beginning on the date of enactment of this Act, including long-term deterioration and reconstruction needs; (3) features that would take advantage of technological capabilities to address modern standards of construction, maintenance, and operations, for purposes of safety, and system management, taking into further consideration system performance and cost; (4) those National Highway System routes that should be added to the existing Inter- state System to more efficiently serve national traffic flows; and (5) the resources necessary to maintain and improve the Interstate System, including the resources required to upgrade the National Highway System routes identified in paragraph (4) to Interstate standards. In carrying out the study, the Transportation Research Boardâ(1) shall con- vene and consult with a panel of national experts, including operators and users of the Interstate System and private-sector stakeholders; and (2) is encouraged to consult withâ(A) the Federal Highway Administration; (B) states; (C) planning agencies at the metropolitan, state, and regional levels; (D) the motor carrier industry; (E) freight shippers; (F) highway safety groups; and (G) other appropri- ate entities. Additional Task Requested by the Federal Highway Administration The study will also consider the role the Interstate System, and modifications to it, can play in providing accessibility for Americans to opportunities such as employment and education and the impact transportation decisions can have on communities and quality of life. These considerations will be examined through case studies and, where quantifiable and appropriate, will be incorporated into cost estimates for reconstructing and expanding the Interstate System.
INTRODUCTION 17 experience, and expertise in highway and transportation system planning; construction, operations, and administration; civil and environmental sys- tems and transportation engineering; economics; law and public policy; traffic safety; and travel and demand modeling (see Appendix A for bio- graphical sketches of the committee members). The committee was immediately occupied by determining how to con- duct a study whose charge entails an examination of such a diverse set of issues, presumes at least some insight into the future, advises on methods to be used for information gathering and analysis, and entrusts the com- mittee with making recommendations on needed changes in law and system resources. The committee conducted several meetings in which it analyzed the study charge and made choices about how best to fulfill it. This task entailed gathering and assessing information and pursuing various avenues of inquiry and analysis, some which proved more fruitful than others. The following sections explain the approach ultimately taken, including the reasons for bounding the study scope and employing certain methods of analysis. The final section of this chapter describes how the report is structured to present the study results. Decisions on the Study Scope Asked to consider future demands on the Interstate System and its expected performance and condition over the next 50 years, the committee had to decide how best to represent the further-out decades of this period, as well as the systemâs broader and potentially evolving role as it connects to and interacts with other highways and transportation modes to move people and goods locally, regionally, nationally, and internationally. The committee recognized that by expanding the study scope in these temporal and spatial directions, it would face significant descriptive and analytic challenges in attempting to account for the many variables and interdependencies arising over long time horizons and across a system whose individual segments and routes have many context- and location-specific functions. The committee decided that, because of these challenges and in light of the paucity of data and modeling capabilities to meet them, it should focus the study on the next two decades when approximating investment needs for the Interstate System, while acknowledging the impracticality of accounting for the many ramifications of these investment choices as they reverberate across other highways and transportation modes. The rationale for these decisions is explained below. Time Frame of Investment Needs Analysis Because the Interstate Highway System consists of many long-lived assets, all decisions about capital investment in the system are by implication
18 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM long-range in nature. Estimating investment needs for the entire Interstate System 50 years into the future, however, would require numerous assump- tions, and much speculation, about many prospective developments and their interactions. The committee concluded that such long-range forecast- ing would yield a wide-ranging, low-confidence set of investment needs estimates having limited value for decision making. It decided instead to narrow its time horizon for estimating these needs to the next 20 years. A number of future uncertainties contributed to this scoping decision, from the countryâs changing population size, composition, and spatial distribution to the nature and pace of technological change, including the prospective development of increasingly automated and connected vehicles and their potential to affect highway demand and supply. The committee also lacked the data and modeling capabilities needed to test a large number of potential future scenarios. Because the modeling systems available for es- timating highway investment needs are designed to inform Congress about near-term (~5 years) spending levels, they depend on baseline information about the condition and performance of the existing highway system. As time passes, one would expect this baseline to become less representative of future conditions. Experience shows that over the longer term, and espe- cially over a period of decades, changes in the condition and supply of high- ways and other transportation modes can have large effects on the level and pattern of travel demand. The Interstate System itself is a testament to this impact, widely credited with spurring the countryâs economic development and expanding metropolitan areas over the past 60 years to affect where, how often, and how far people drive and use other transportation modes. Having little choice but to use available models to estimate future in- vestment needs for the Interstate System, the committee was reluctant to apply them to a period beyond 20 years, when the cumulative effect of these demand and supply interactions is likely to be substantial. A 20-year time frame also involves a great deal of uncertainty for modeling, particularly for estimating capacity-related investment needs that will depend on future levels of travel on the Interstate System. Significant capacity additions will likely be required over this period because of growth of urban areas that are not well connected to the Interstate System and because of the contin- ued growth of large metropolitan regions. The size, location, and timing of these needed additions will depend on a host of factors related to changes in the population and economy, how travelers respond to congestion and the supply of new capacity, and the availability of options other than In- terstate travel. Yet, the systemâs future over the next 20 years is not imponderable. Over this period, the system can reasonably be expected to experience increasing demand in line with a growing population and economy, with much of this demand taking place on urban segments of the Interstate
INTRODUCTION 19 System that are already heavily used and projected to account for most of the countryâs population growth. Although increasingly automated and connected vehicles may be entering the fleet, their impacts on travel demand should be marginal over most of the time frame. By stretching the national- level modeling capabilities that exist and using a range of travel growth rates indicative of recent travel behavior, the committee concluded that it could at least make rough approximations of the magnitude of spending that might be needed for capacity-related improvements over the next 20 years. Moreover, during this period, the cost of repairing and reconstructing Interstate assets that have already incurred significant deterioration from the effects of age and past use will be coming due, and these costs can be modeled with greater confidence. Relationship of Interstates to Other Highways and Modes The Interstate Highway System accounts for about 25 percent of all VMT nationwide in the country, and an even larger share of travel for longer- distance movements of high-value freight. The urban portions of the system have become commuter corridors that have shaped the pattern of metro- politan land development and the use and configuration of other local and regional transportation systems, such as public transit. Interstates connect the countryâs nearly 400 metropolitan areas, and in many cases are the only available means of transportation for intercity and interregional trips between neighboring metropolitan areas 50 to 200 miles apart (TRB 2016). By connecting with airline, marine, and rail terminals, the Interstates are a vital part of the countryâs intermodal freight system, sometimes used for moving traffic short distances to and from these terminals and at others times for longer-haul movements to and from them. Depending on the lo- cation and purpose of travel, the Interstates connect to, compete with, and complement other highways and transportation modes from public transit and airline service to passenger and freight rail. Full and accurate depictions and analyses of the role of the Interstate Highway System would account for its many functions across the passen- ger and freight transportation domains and at the local, interregional, and longer-distance levels. They would also take into account how these func- tions differ by specific locationâfor instance, depending on the availability of substitute and complementary modes (e.g., passenger rail for intercity travel and urban rail for commuter service)âand by specific transportation purpose, for instance, depending on the time-sensitive nature of passenger trips and freight movements. Such an accounting of the Interstate Systemâs role within the broader transportation system, including its impact on other highways and their use, would be far more revealing about system investment needs and impacts than analyses focused on the system as if it
20 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM functioned alone. The committee recognizes the desirability of assuming such a broad and comprehensive perspective on the Interstate Highway System, but could think of no practical way to do so for the purpose of estimating investments needs and their impacts. As is the case for estimating longer-range investment needs, neither the data nor the modeling capabilities required to allow for rich depictions and analyses of the Interstate Highway Systemâs role within the broader transportation system exist at the national level. For example, the only national-level database on longer-distance passenger travel that includes highway trips is the American Travel Survey, which was last updated more than 20 years ago. Inasmuch as the Interstate highways are the main con- duits for long-distance travel, this data gap, which has been documented in other reports (TRB 2011, 2016), limits understanding of the Interstate Systemâs functionality and interconnectivity with other modes. While some states and metropolitan planning organizations have travel survey data and models that disaggregate travel by activity (e.g., commuting versus shop- ping), the state- and metropolitan-specific nature of these data and models do not lend themselves to extrapolation over the entire Interstate System for the purpose of estimating system-level investment needs. While reflecting these practical reasons for limiting the scope of this study to the Interstate Highway System when estimating investment needs, this report does not lose sight of the systemâs impacts on the rest of the countryâs transportation system and its elements. In considering its rec- ommendations, for instance, the committee was cognizant of this wider impact on matters ranging from how investments in the Interstate System are funded so as not to disadvantage or draw resources from other modes to concerns about how a congested and physically deteriorating Interstate System could adversely affect the intermodal freight system. Methods of Analysis Outside Consultations Asked to seek input from outside experts and parties, and recognizing the importance and value of such consultation, the committee scheduled a num- ber of public sessionsâboth in conjunction with full committee meetings and as part of subcommittee meetings held in locations across the country. Speakers were invited to provide information and their views on the issues included in the study charge. Participants in these sessions included but were not limited to â¢ Officials from FHWA and state transportation agencies and metro- politan planning organizations, as well as federal, state, regional, and local authorities having related responsibilities;
INTRODUCTION 21 â¢ Representatives of urban transit systems, the trucking and shipping sectors, and the automobile industry; â¢ Experts in public policy, economics, and engineering and those with prior highway transportation experience; â¢ Experts in the technology of highway construction, vehicles, en- ergy, telecommunications, and other relevant fields and industries; â¢ Practitioners of travel demand modeling and forecasting; â¢ Individuals and organizations advocating for energy conservation, community and environmental interests, and traffic safety; and â¢ Experts in transportation infrastructure funding and financing and the role of transportation in supporting national security logistics. The more than 100 individuals who met with the committee are listed in Appendix B. Included among them were officials from 16 state DOTs; 5 other public transportation agencies; 4 federal agencies; 5 corridor coali- tions; 6 metropolitan, regional, or civic planning organizations; 2 city gov- ernments; 1 tribal transportation committee; 16 private-sector companies; 14 industry associations and nonprofit organizations; and 17 think tanks and universities. In addition, time was allocated at public meetings for com- ments by members of the general public. The extent of interest in the study from such a wide range of parties reflects the Interstate Systemâs social and economic importance. Further- more, these consultations gave the committee a deeper appreciation of the impact and importance of the Interstate System to the economy and the daily lives of Americans. These outside consultations reinforced the committeeâs initial concern that certain aspects of the study charge would be difficult to address in a direct and meaningful way. For instance, after meeting with experts in highway and vehicle technologies, the committee concluded that it would be unwise, or even impossible, to pursue an in-depth examination of the potential for technology to bring about new capabilities that would enable the application of new standards of construction, maintenance, and opera- tions and safety over the entire 50-year period of interest to the study. In examining the feasibility of performing such an examination, the com- mittee acknowledged that technological progress will indeed lead to new and improved capabilities affecting each of these matters, and that these developments will temper some of the challenges that lie ahead in readying the Interstate Highway System for the future. In the past 20 years alone, there has been a revolution in intelligent transportation systems, highway materials such as ultra-high-performance concrete and corrosion-resistant steel reinforcement, and construction methods such as accelerated bridge construction. At the same time, however, predicting specific technological developments in the more distant future appeared to be a far-ranging and
22 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM potentially speculative exercise that the committee could not envision yield- ing a productive outcome. Similarly, even after hearing from many presenters about the impor- tance of the Interstate Highway System to the economy and the daily lives of Americans, the committee could think of no good way to respond in a direct manner to the call for an examination of the systemâs future impact on access to employment and education or on communities and quality of life. The Interstate System is multipurpose, operates on a number of spatial scales, and serves a broad array of users, including commuters, shoppers, and commercial-service trucks traveling locally; people making leisure and business trips from one region to another; and long-haul freight trucks car- rying a wide range of goods. In each case, the Interstates are part of a larger network of highways and transportation modes, some that are complemen- tary and others that are substitutes, depending on the nature and purpose of the trip. In light of the Interstatesâ varied and often context-specific roles, the committee recognized that an examination of the systemâs functioning in relation to other transportation modes in serving such purposes as provid- ing access to employment, education, and social activities would require a more granular review than could be provided in this national-level study. The original planners and builders of the system expected it to have such far-reaching impacts, although they may have discounted the potential for some undesirable outcomes. While the committee gathered much infor- mation and heard many opinions about the Interstatesâ past and current impacts in these areas, it could think of no good way to undertake a pro- spective economic and social assessment of a system that is already in place and integrated into the countryâs economic and social fabric. Given that integration, however, it is fair to say that the systemâs safe, efficient, and reliable operations will be critical to its continued ability to confer crucial economic and social benefits, and that traditional measures of system per- formance, such as vehicle-to-capacity ratios, crash rates, and person-hours of delay, can offer reasonable indicators of success. Commissioned Resource Papers On some important matters, the committee recognized a need for additional information and expert analyses that could not be obtained through brief- ings alone and that exceeded its membersâ subject matter expertise. The committee therefore commissioned several resource papers to inform its de- liberations and provide the basis for the reportâs discussion of certain major developments expected to have important implications for the use, condi- tion, performance, investment needs, and funding of the Interstate System. These resource papers, which are provided in Appendixes C through G, consider such issues as the countryâs future demographic and economic
INTRODUCTION 23 development and the implications for motor vehicle travel, prospects for a dramatically changing climate, and the consequences of technological advances for the vehicle fleet. Modeling As stipulated by Congress, the committee consulted the report of NCHRP Project 20-24(79) with respect to the methodology proposed therein for es- timating the improvements and investments needed to renew and modernize the Interstate Highway System in the coming decades. The NCHRP report proposes a four-step process for developing these estimates. The first is es- timating the investments needed to restore the existing system to a state of âgood repairâ through targeted resurfacing, restoration, rehabilitation, and reconstruction work.1 The second step is estimating the additional invest- ments in designs and technologies required to ensure that this restored sys- tem operates efficiently through optimized use of its current capacity. The third step is estimating investments that can be made to increase operating capacity through physical changes, including adding lanes and improving interchanges. The final step calls for application of advanced highway and vehicle technology and demand management methods to increase the sys- temâs capacity. The NCHRP report proposes the use of FHWAâs long-standing highway and bridge investment modeling systemsâthe Highway Economic Require- ments System (HERS) and National Bridge Investment Analysis System (NBIAS)âfor the development of these investment estimates. These models, which are described in greater detail in Appendix H and Chapter 5, are used to perform benefit-cost calculations to determine when an improvement is justified. This is accomplished by calculating the expenditure required to make a given improvement, the condition and performance impact of the improvement (e.g., on pavement smoothness, deck condition, and peak vehicle capacity), and benefits to traffic operations derived from the im- proved condition and performance. However, the NCHRP report also rec- ognizes that these two models consider only a limited set of improvements. The report therefore proposes that the model results be supplemented with information derived from project case studies and other analytic tools. In accordance with the wishes of Congress, the committee commis- sioned a series of analyses of HERS and NBIAS to test whether the four-step 1 Resurfacing, restoration, and rehabilitation (3R) projects usually involve pavement im- provements intended to preserve and extend the service life of existing highways and improve safety. Restoration and rehabilitation work includes such repairs as strengthening roadway bases, shoulder work, and drainage work that enable additional treatments, such as resurfac- ing, to be done. They typically involve maintaining the existing three-dimensional alignment. âReconstructionâ is defined as rebuilding roadways primarily along existing alignment.
24 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM progression of layered improvements described above would enable the de- termination of investment needs for the future Interstate System. Based on information in the commissioned resource paper on future traffic growth, the models were run using rates of VMT growth ranging from 0.75 to 2.0 percent annually for a period of up to 20 years, as well as for a longer time frame. These analyses led the committee to conclude that the models are not sufficiently robust for investment planning beyond approximately 20 years. The committee also concluded that the proposed four-step progres- sion of investment choices was not a useful approach because decisions on Interstate investments are generally not made on the basis of well-defined calculations of benefits and costs. If they were made in this manner, more- over, they almost certainly would not focus on a prescribed sequence of specific improvement types. Rather, they would generate an ordering based on the most cost-beneficial improvements regardless of type. Having determined that it would not follow the NCHRP proposal strictly, the committee nevertheless made considerable use of HERS and NBIAS. As a practical matter, there are no substitutes for these systems for providing baseline information on the current condition and performance of the Interstate Highway System. Nor are there substitutes for predicting how changing the level of traffic affects the condition and operating per- formance of the Interstate System or for estimating the expenditure level associated with specific types of highway and bridge improvements. Thus, while the modelsâ values, algorithms, and output are sometimes simplistic (in ways noted elsewhere in this report), the two models nevertheless areâ with some supplementation by other analytic tools2âsufficient in the com- mitteeâs view for making approximations of the investment levels needed over the near to medium terms. Thus, to make use of HERS and NBIAS required applying plausible rates of traffic growth over the next 20 years and using the models to identify Interstate highway improvements that would be cost-beneficial. Candidate improvements having a calculated benefit-cost ratio of 1 or more would then be categorized as a sound investment and included when calculating total investment requirements. The total is indicative of invest- ment needs in the system; however, it ultimately falls on decision makers to determine whether the investments levels are warranted in light of other demands on resources and in relation to public expectations for levels of traffic delay and pavement and bridge condition. In sum, the committee acknowledges the limitations of the HERS and NBIAS models regarding levels of system condition and performance, mea- surement of benefits and costs, and basic algorithms employed. Nonetheless, 2 The Pavement Health Track (PHT) tool was used to supplement HERS output data. The tool and the analysis are described in Chapter 5.
INTRODUCTION 25 in keeping with Congressâs request for a study employing the methods proposed in the NCHRP report, which center on these models and whose results are routinely presented to Congress, the committee used the models to the extent possible. Case Studies Finally, pursuant to the NCHRP proposed methodology, the committee commissioned a set of nearly two dozen case studies of ongoing and planned Interstate projects. These case studies, which are presented in Appendix I, illustrate improvements to the Interstate System currently being made and those that will be needed in the future. The various projects examined in the case studies also provide some additional real-world cost information that could be used to evaluate the cost data obtained from other sources and the analytical models. The case studies, however, did not play as important a role in estimating future system investment needs as originally anticipated because of the difficulty of generalizing from a small number of projects. REPORT ORGANIZATION The remainder of this report is organized into six chapters. It is accompa- nied by appendixes included herein, as well as selected online appendixes. Chapter 2 provides additional background and context for the study, including a discussion of the history of the Interstate highway program that explains its original purpose, structure, and evolution. Chapter 3 identi- fies and examines pressing and emerging challenges that, in the commit- teeâs view, decision makers will need to confront to prepare the Interstate Highway System for the future. These challengesâranging from the need to rebuild the systemâs foundation to preparing for climate change and the substantial infusion of new technologyâwere gleaned from the com- mitteeâs outside consultations, the commissioned resource papers, and the expertise and professional judgment of its members. Trends and factors that will shape the nature and magnitude of these critical challenges, from the nationâs changing population to the expectations of transformative vehicle technologies, are addressed in Chapter 4. The special analyses performed by or for the committee are the basis for Chapters 5 and 6. The analysis described in Chapter 5 employed the HERS and NBIAS models, along with some off-model tools and methods, to determine an approximate range of annual investment levels that will be required over the next 20 years to place the Interstate System on a course to meet the critical challenges identified in Chapter 3. The modeling and other analyses reported in Chapter 5 are but a fraction of those that were conducted, but are the most relevant to this study. Chapter 6 reviews the
26 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM means by which the Interstate System is currently funded and how revenues are allocated. Importantly, this chapter and the complementary Appendix J examine funding options and provide estimates of how each option could generate the revenue levels required to fund the 20-year investment needs identified in Chapter 5. After summarizing the committeeâs findings, based on the information, analyses, and assessments contained in earlier chapters, Chapter 7 presents a blueprint for action to maintain the National System of Interstate and Defense Highways as the countryâs premier transportation system. To this end, the chapter offers 10 recommendations for policy change. REFERENCES Abbreviations FHWA Federal Highway Administration TRB Transportation Research Board Edwards, A. 2018. Hiding in Plain Sight: The FDR Interstate Highway Map. National Archives: The Unwritten Record, June 26. https://unwritten-record.blogs.archives. gov/2018/06/26/hiding-in-plain-sight-the-fdr-interstate-highway-map. FHWA. 2014. Highway Statistics 2014: Public Road Mileage-MVT-Lane Miles, 1920â2013. https://www.fhwa.dot.gov/policyinformation/statistics/2013/vmt421c.cfm. FHWA. 2017a. Public Road Length by Functional System and Federal-Aid Highways. Table HM-18. https://www.fhwa.dot.gov/policyinformation/statistics/2016/hm18.cfm. FHWA. 2017b. Highway Statistics 2016: Annual Vehicle-Miles of Travel, 1980â2016. Table VM-202. https://www.fhwa.dot.gov/policyinformation/statistics/2016/pdf/vm202.pdf. Miller, D., S. Binder, H. Louch, K. Ahern, H. Kassoff, and S. Lockwood. 2013. Specifica- tions for a National Study of the Future 3R, 4R, and Capacity Needs of the Interstate System. NCHRP Project 20-24(79). http://onlinepubs.trb.org/onlinepubs/nchrp/docs/ NCHRP20-24(79)_FR.pdf. TRB. 2011. Special Report 304: How We Travel: A Sustainable National Program for Travel Data. Transportation Research Board, Washington, D.C TRB. 2016. Special Report 320: Interregional Travel: A New Perspective for Policy Making. Transportation Research Board, Washington, D.C.