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4 Confronting an Uncertain Future The previous chapter identifies current and emerging challenges that face decision makers seeking to renew, rightsize, and modernize the Interstate Highway System. A number of these challenges have been recognized for some time, while others have attracted attention only recently. Described in Chapter 3 as they are understood today, the challenges may appear quite different in the future as user demands, technological capabilities, economic and environmental conditions, and other circumstancesâincluding policy choicesâchange. This chapter reviews some of the likely areas of change that together contribute to a future that is uncertain, but with which deci- sion makers will nonetheless have to contend as they make choices about where, when, and how much to invest in expensive and long-lived assets included in the Interstate Highway System. As discussed in Chapter 1, the study committee commissioned five resource papers (see the appendixes) that consider how the future may evolve with regard to several developments likely to substantively impact the Interstate System: â¢ Chi (see Appendix E) examines how a changing U.S. population and its spatial patterns could affect demand for Interstate highways in different parts of the country. â¢ Sieber and Weisbrod (see Appendix D) consider how the scope of this demand could be affected by spatial and sectoral changes in the economy. â¢ After reviewing past influences on travel demand, Polzin (see Appen- dix C) discusses how the combination of changes in demographics, 85
86 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM economic activity, technology, and other factorsâincluding the availability of alternatives to highway travelâcould translate into differing rates of growth in motor vehicle travel demand in general and on the Interstate System specifically. â¢ Shladover (see Appendix F) considers how the development and deployment of connected and automated vehicle technology could affect both the supply and demand sides of transportation and the Interstate System. â¢ Wuebbles and Jacobs (see Appendix G) examine how climate change and its consequences could impact the Interstate Systemâs condition, performance, and use. These papers confirm that some developments, such as population growth rates and their spatial dimensions, can be forecast substantially bet- ter than othersâespecially technology change. In each case, however, un- certainties about the magnitude, direction, and nature of change complicate the prediction of future demand and supply for the Interstate System. This complexity is compounded by the interaction among such developments. As noted in the previous chapter, the original planners of the Interstate System failed to estimate how the system would be used and perform just two decades after it was approved by Congress. Although informed by fairly accurate forecasts of the U.S. population, planners in the 1950s had little insight into how important emerging demographic, economic, and policy changesâsuch as much larger numbers of women driving, marked growth in international trade, and large increases in allowable truck weights and truck trafficâwould affect their predictions. Even today, transportation planners are adjusting their near-term travel forecasts to account for un- anticipated changes in information and communication capabilities that have allowed more workers to telecommute; enabled online shopping with more home delivery of goods; and provided travelers with more informed, real-time modal and routing options. The first section that follows presents a review of U.S. population forecasts, both for the country as whole and for geographic regions, down to the level of counties. Although county-level population forecasts involve greater uncertainty relative to those at higher levels, they provide insights into how the Interstate Systemâs scope and its proximity to, and connections with, communities could change over the next 40 years. Perhaps more than any other future development, population growth and its spatial patterns can be assessed with a reasonable degree of confidence, and related to the Interstate System and demand for changes to its geographic coverage. Because demand will depend on more than the size and distribution of
CONFRONTING AN UNCERTAIN FUTURE 87 population, this section also considers how sectoral, compositional, and locational shifts in economic activity among regions could have implica- tions for demand for access to the Interstate System. As discussed in Chapter 3, between 1980 and 2015, vehicle-miles traveled (VMT) on the Interstate System grew by more than 160 percent, compared with a 90 percent increase on all other public roads. If both the U.S. population and the economy grow over the next several decades, as can be reasonably expected, growth in highway travel will almost certainly ensue, and the Interstate System as a whole will likely become more heavily used. While reasonable projections of the growth of the population and the economy can be made, they need to be accompanied by assumptions about the composition of this growth so it can be related to changes in highway demand. Whether the growing population is older or younger, living in smaller or larger households, and concentrated more or less in urban or ru- ral areas all will affect demand. Likewise, a growing economy that is more or less goods- or service-oriented or that involves more or less trade will be accompanied by different patterns and levels of travel. The second section of the chapter therefore considers how future changes in the U.S. popula- tion and economy could interact with one another and with other factors related to travel behavior to affect growth in passenger and freight travel generally and on the Interstates specifically. These rates of growth will have implications for system capacity demands and for wear and deterioration of pavements and bridges, and because of the significant uncertainties in- volved, must be forecast within a range of confidence. The third and fourth sections of the chapter consider developments in two key areas that are expected to have profound effects on the Interstate Highway System, but whose timing and nature cannot be forecast and as- sessed in the same manner as changes in population and the economy. The first of these areas is major technological changes, the most prominent of which is the prospect of large-scale deployment of connected and auto- mated vehicles. The second key area is a dramatically changing climate and its environmental consequences, which could lead to major economic and social disruptions. Because both an increasingly automated transportation system and climate change are considered highly likely, contemplating a future Interstate Highway System without considering their potential im- pacts would be untenable. While the future changes in these areas cannot be assessed in detail, these two sections of the chapter review a range of possible outcomes that can inform near-term decision making.
88 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM CHANGING CENTERS OF POPULATION AND ECONOMIC ACTIVITY At a Glance â¢ The historical trend of strong population growth in the West and South has continued into the present century. States in these regions can be expected to see increased demand for access to the Interstate System. Geographically uneven growth will exacerbate this pressure and the access disparities among regions. â¢ Projections point to some significantly growing counties that cur- rently do not have access to an Interstate highway. This section focuses on how forecast spatial and sectoral changes in the U.S. population and economy are likely to affect demand for modifications to the scope of the Interstate highway network. Decisions about where to extend the length of the Interstate System, or in some cases perhaps redes- ignating segments, will entail consideration of national- and network-level passenger and freight traffic flows. Scope of the Interstate System and the Changing Geography of the U.S. Population While the demand for access to the Interstate System is affected by factors other than adjacent population, travel demand is highly correlated with population. As shown in Table 4-1, the historical trend of strong popula- tion growth in the West and South has continued into this century, with these regions growing approximately four times as fast as the Northeast and Midwest. During this period, six statesâArizona, California, Florida, Georgia, North Carolina, and Texasâcollectively accumulated more than 50 percent of the population growth nationwide. Given the increase in VMT on the Interstate highways in the past few decades compared with TABLE 4-1 U.S. Population Change by Census Region Census Region Net Change 2000â2016 (%) Northeast 4.9 Midwest 5.5 South 22.0 West 21.3 U.S. Total 14.8 SOURCE: U.S. Census Bureau 2016.
CONFRONTING AN UNCERTAIN FUTURE 89 that on other roads, continued geographically uneven growth is likely to exacerbate disparities in Interstate access among regions. The Census Bureau forecasts the U.S. population over multiple time frames and for various aspects of its composition (e.g., age, sex, race, and ethnicity). These forecasts can be used to develop county-level projections of demand for the Interstate System over the next 40 years as the size and density of the countryâs population change spatially. Figure 4-1 shows the population size and density by county as of 2010 and projected patterns of change by 2060. Based on the Census Bureauâs midrange forecasts, total U.S. population will grow by 37 percent (from 310 million to 426 million) during this period, with population growth areas being concentrated in Arizona, California, Colorado, Florida, Hawaii, Oregon, southeast Texas, Utah, Washington, counties on the metropolitan east coast, and a tri- angular area between Atlanta, North Carolina, and Nashville. Remarkably, the number of counties, mostly rural, that are projected to experience a population decline is larger than the number of counties forecast to gain population. The former counties are principally in the northeast corner to the Appalachian region; bordering the Great Lakes, except Lake Michigan; along the Mississippi River; the Deep South states; and Alaska. Superimposing a map of the current Interstate System on the projected populations and population densities of counties in 2060 (see Figure 4-2) indicates that more heavily and densely populated counties will, with a few exceptions, be connected by the system as it exists today. At present, a total of 1,444 out of 3,142 counties are served by the Interstate System. When counties that fall within 20 miles of the system are included, 2,477 can be considered to have access and 665 to lack access. The projected average population of counties with access to the system in 2060 is 161,800, com- pared with an average population of 21,400 for counties lacking access. The populations of counties located within 20 miles of the Interstate System are projected to grow by an average of 42,750 by that year, compared with only 1,060 in counties located more than 20 miles from the system. These county-level projections for 2060 assume that population growth will be particularly strong along I-5 from Washington to San Diego; along I-10 from Los Angeles to Phoenix; along I-40 from Los Angeles to Albu- querque; along I-15 from Los Angeles to Utah; along I-20, I-35, and I-45 spreading from Dallas; along I-20 from San Antonio to Pensacola; along I-75 and I-95 in southern and central Florida; along Interstates in the tri- angle of Atlanta, North Carolina, and Nashville; along I-95 from Washing- ton, DC, to Boston; and along I-90 and I-94 from Minneapolis to Detroit (Chi [see Appendix E]). While this analysis indicates that population will continue to grow the most in areas already served by or connected to the Interstate System, the projections also point to some growing counties that do not currently have
90 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM (a) Population Change (b) Population Density Change FIGURE 4-1 Population change (a), population density change (b), and percentage population change (c), 2010â2060. SOURCE: Chi (see Appendix E).
CONFRONTING AN UNCERTAIN FUTURE 91 access to an Interstate highway (although some of these counties may be located within 20 miles of one). Figure 4-3 shows the counties projected to rank among the top 50 percent of counties in population growth rate and population density from 2010 to 2060 that do not currently have an Interstate highway within their borders. These counties are scattered from the northwest corner of Washington State to the west of Colorado; from the southeast corner of New Mexico to Houston; the tristate area of Montana, South Dakota, and North Dakota; northwest North Dakota; and Hawaii. Scope of the Interstate System and the Changing Geography of Economic Activity The United States is forecast to continue to enjoy overall economic growth over the next several decades, perhaps along the lines of historical increas- es.1 While economic growth drives overall traffic growth, it also tends to be accompanied by changes in the location of economic activity (McMullen and Eckstein 2012). Growing economic activity and changes in its location can have far-reaching effects on the amount and mix of automobile and 1 The U.S. national economy is expected to grow moderately through 2046, with real gross domestic product (GDP) projected to increase at an average annual rate of 2.0 percent. Over the same period, real disposable income per capita is projected to grow at a slightly slower annual rate of 1.6 percent (FHWA 2018a). (c) Percentage Population Change FIGURE 4-1 Continued
92 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM FIGURE 4-2 Projected population and population density in 2060 compared with the current Interstate Highway System. SOURCE: Chi (see Appendix E). (a) Projected Population (b) Population Density
CONFRONTING AN UNCERTAIN FUTURE 93 truck traffic, on average trip distances, and on the originâdestination pat- terns of that traffic. The core drivers of the U.S. economy are basic industriesâsuch as mining, agriculture, forestry, manufacturing, and technology and supply chain servicesâthat locate where it is most feasible and profitable to do so because they produce goods or services sold widely, across the nation or internationally (Seiber and Weisbrod [see Appendix D]). Their composition, as well as their location, will of course change over time, which in turn will affect the spatial distribution of employment and income. Population growth follows changes in job opportunities in these basic industries, which affect growth in other, more localized industries, such as education, health care, retail sales, and personal services. If the shift to an information econ- omy continues, the growing urbanization of recent decades will also persist. Figure 4-4 shows schematically how these basic relationships translate further into changes in automotive travel and trucking activity. More em- ployment leads to more commuter trips (AASHTO 2013; see also Sieber and Weisbrod [see Appendix D]). Higher income due to employment growth leads to greater consumption of goods and attendant demand for freight transportation, as well as to increases in the purchase of automobiles and their use for social and recreational trips. Increasing regional economic FIGURE 4-3 Counties projected to be among the top 50 percent of counties in population growth rate and density that lack an Interstate highway. SOURCE: Chi (see Appendix E).
94 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM specialization in the basic industries can result in even more shifting of the originâdestination pattern of goods and services, with implications for the split of freight mode share and for the location and length of freight trips. More regional specialization also tends to lead to longer shipping distances and to resultant increases in truck traffic on the trunk corridors of the In- terstate Highway System. Figure 4-5 shows how the spatial pattern of job growth in the United States shifted from 1985 to 2015, leading to employment and income losses in some parts of the country and increases in others. While the strength of the relationship among employment, income, and VMT is considered in more detail later in this chapter, that positive relationship supports the conclusion that as changes in the geography of the population occur, the de- mand for highway access may not align with the existing Interstate System. Changes in the amount and location of economic activity are not the only drivers of change in demand for highway access; the changing compo- sition of the activity is a factor as well. There are key differences in highway use among industries, particularly in the extent to which they generate truck VMT (see Table 4-2). These differences in highway use among industries can combine with shifting spatial patterns of economic activity to have important implications for the use of highways for freight movement. A measure termed âfreight intensityââdefined as the tonnage of freight per job by industry relative to the national average for all industriesâindicates how regional changes in employment within an industry can translate into differences in freight demand (Sieber and Weisbrod [see Appendix D]). Figure 4-6 shows changes in freight intensity relative to the U.S. average between 1985 and 2015, affecting changes in industry mix. It is evident that changes in both the location and composition of economic activity have importantâand difficult-to-predictâimplications. FIGURE 4-4 How changes in the economy affect car and truck vehicle-miles traveled. NOTE: OâD = originâdestination. SOURCE: Sieber and Weisbrod (see Appendix D).
CONFRONTING AN UNCERTAIN FUTURE 95 The Census Bureau provides forecasts of future population by region that can be used to estimate demand for access to Interstate highways. However, forecasting changes in the size and composition of economic activity that will accompany and help drive these population shifts and resultant transportation demand requires consideration of more variables. A set of alternative future scenarios can provide insight into the effects of a changing economy on demand for travel on highways, including Interstates. The scenarios examined for this study employ widely used demographic and economic forecasts of changes in population, number of households, household size and location, workforce size, number of retirees and chil- dren, employment, and worker income generated for more than 50 indus- try sectors. The scenarios differ in assumptions as to which variables will influence economic growth and composition, such as the rate of growth in global markets, productivity, and energy and other resource prices, along with inflation and interest rates. The base-case scenario leads to an expectation of 42.5 million more jobs in 2045, but with higher-than-average job growth in only 13 industries. Figure 4-7 shows the expected impact of these patterns of industry job growth on population growth, including growth in jobs in service industries that follow shifts in basic industries. Counties forecast FIGURE 4-5 Change in employment by county, 1985â2015. SOURCE: Sieber and Weisbrod (see Appendix D).
96 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM TABLE 4-2 Differences Among Industries in Tonnage, Truck Reliance, Shipment Distance, and Value Industry Tonnage (Millions) Tons per Employee % by Truck % by Mult. Modes* Miles per Shipment Value per Ton ($1,000s) Crop Production 1,493 992.5 80.6% 2.4% 637.3 357 Animal Production 237 202.7 91.7% 1.6% 715.6 1,060 Forestry and Logging 337 2,321.1 91.3% 0.1% 1,521.2 49 Fishing, etc. 6 58.0 93.2% 1.9% 366.1 1,349 Oil and Gas Extraction 778 956.9 29.2% 0.5% 77.5 721 Mining, Quarrying, and Support 4,133 5,379.6 61.7% 2.6% 353.7 74 Food Manufacturing 985 545.1 88.5% 2.6% 545.9 1,125 Beverage and Tobacco Product Manufacturing 185 747.1 90.5% 3.1% 315.0 1,658 Textile Mills and Products Manufacturing 33 134.4 88.8% 6.7% 268.2 8,569 Apparel Manufacturing 10 58.0 89.0% 9.2% 340.6 12,996 Leather Product Manufacturing 4 105.4 87.3% 11.6% 613.1 12,594 Wood Product Manufacturing 430 962.5 89.5% 3.1% 787.4 574 Paper Manufacturing 246 653.2 82.5% 3.4% 808.2 982 Printing 18 32.0 92.0% 6.7% 406.5 4,190 Petroleum and Coal Products Manufacturing 3,845 33,362.4 34.1% 0.6% 179.4 596 Chemical Manufacturing 761 963.7 61.8% 2.9% 331.6 2,390 Plastics and Rubber Products Manufacturing 107 151.8 78.4% 4.3% 649.2 3,252 Nonmetal Mineral Product Manufacturing 1,029 2,403.3 92.0% 1.7% 488.7 205 Primary Metal Manufacturing 375 924.0 79.8% 3.9% 731.9 1,218 Fabricated Metal Manufacturing 235 155.3 89.4% 3.1% 543.4 2,409 Machinery Manufacturing 123 107.8 91.9% 3.3% 2,181.7 5,958
CONFRONTING AN UNCERTAIN FUTURE 97 Industry Tonnage (Millions) Tons per Employee % by Truck % by Mult. Modes* Miles per Shipment Value per Ton ($1,000s) Computer and Electronic Manufacturing 53 54.3 87.8% 8.9% 333.1 19,062 Electrical Equipment and Appliance Manufacturing 40 99.1 92.1% 4.6% 785.6 10,803 Transportation Equipment Manufacturing 270 167.6 85.0% 5.1% 381.2 5,461 Furniture Manufacturing 55 130.5 95.8% 1.6% 408.6 4,903 Miscellaneous Manufacturing 72 106.2 88.5% 6.8% 274.5 7,835 Wholesale Trade 384 59.6 96.3% 1.5% 431.8 3,644 Media and Information 19 5.5 92.3% 6.2% 361.0 4,111 Business Services 248 20.7 92.6% 1.7% 517.3 123 NOTE: * = Multiple modes include truckârail, truckâair, and truckâmarine shipments. SOURCE: Sieber and Weisbrod (see Appendix D). TABLE 4-2 Continued FIGURE 4-6 Changes in freight intensity relative to the U.S. average by county, 1985â2015. SOURCE: Sieber and Weisbrod (see Appendix D).
98 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM to have higher-than-average growth include some areas that are already fast-growing, including southern California, the San Francisco Bay Area, the Texas triangle, southern Florida, and certain other metropolitan areas. Such a pattern would be expected to add further to demand for highways in the countryâs metropolitan areas and megaregions. Figure 4-8 shows how this geographic pattern of industry growth could lead to changes in freight intensity (relative to the U.S. average change), thus shifting demand for truck transportation. The forecast pattern of industrial activity indicates growing freight intensity in parts of the West, South, and Southeast/Mid-Atlantic regions. Because of uncertainty about future economic changes, the committee considered alternative scenarios that, for instance, assume stronger U.S. economic prosperity, protracted economic slumps, and lower fuel and transportation costs (see Figure 4-9). The expected impacts of lower fuel and transportation costs on freight volumes vary significantly across indus- tries to affect portions of the highway network differently. For instance, FIGURE 4-7 Forecast change in employment by county, 2015â2045. NOTE: CAGR = compound annual growth rate. SOURCE: Sieber and Weisbrod (see Appendix D).
CONFRONTING AN UNCERTAIN FUTURE 99 reductions in freight tonnage (blue lines in Figure 4-9) would be expected on highway routes in areas that experience reduced demand for energy, such as states that produce petroleum and shale oil that are adversely af- fected by lower fuel prices. Conversely, increases in freight tonnage (red lines in the figure) would occur under this scenario on highway routes where manufacturers and shippers benefit from the lower energy prices to gain productivity and profitability. While similar calculations and visualizations can be prepared for other scenarios, the purpose of this exercise was to illustrate how a changing economy, coupled with changing demographics, can have important impli- cations for demand on the Interstate Highway System. Keeping pace with the countryâs economic and demographic changes is important to ensure that the Interstate System is configured to meet new spatial and capacity demands for passenger and freight traffic. In the next section, the committee considers economic, demographic, and other developments that may trans- late into changes in travel demand, specifically on the Interstate System, over the next several decades. FIGURE 4-8 Forecast change in freight intensity relative to the U.S. average by county, 2015â2045. SOURCE: Sieber and Weisbrod (see Appendix D).
100 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM FUTURE TRAVEL DEMAND AND THE INTERSTATE SYSTEM At a Glance â¢ Some of the factors that drove vehicle-miles traveled (VMT) dur- ing the last half of the 20th century are no longer impactful, while new ones have emerged that could have significant relevance to future travel trends. â¢ The moderation of travel demand growth that began in the early 2000s is presumed, but not entirely proven, to be associated with a cyclical decline in the economy (Great Recession), thereby com- plicating the forecasting of future trends in travel. â¢ Continuation of past trends in VMT demand on urban Inter- states would result in large increases in travel on urban systems that would further tax their already stressed capacity. The policy choices associated with such capacity expansion will entail com- plex social, environmental, and financial considerations. FIGURE 4-9 Changes in freight flows for a future scenario with lower fuel and transportation costs. SOURCE: Seiber and Weisbrod (see Appendix D).
CONFRONTING AN UNCERTAIN FUTURE 101 The factors that have historically influenced trends in motor vehicle travel, at least over the past half century, have been well studied and provide in- sight into how travel trends will change in the future and affect the use of Interstate highways. Past trends in VMT have been influenced by numer- ous factors, many of which (e.g., rising income, population growth) should continue to influence future travel demand. Conversely, some factors that drove VMT during the last half of the 20th century (e.g., women entering the workforce in larger numbers) are no longer impactful, while new ones (e.g., e-commerce, retiring baby boomers) have emerged that could have significant relevance to future travel trends. Figure 4-10 shows the long-term trends in VMT and U.S. population growth since 1900. Annually, from 1945 through 2005, VMT increased at an average rate of more than 4 percent, while population grew by slightly more than 1 percent. During that same period, the annualized rate of growth in gross domestic product (GDP) was slightly more than 3 percent. For much of this 60-year period, major changes were taking place in both the American economy and society that contributed to the higher rate of growth in VMT relative to population. These changes included women joining the workforce and becoming licensed to drive in large numbers; the FIGURE 4-10 Annual U.S. trends in growth in vehicle-miles traveled (VMT) and population, 1900â2016. SOURCE: Polzin (see Appendix C).
102 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM baby boom cohort reaching adulthood and forming households; and the postâWorld War II acceleration of the decentralization and suburbanization of metropolitan areas, spurred in part by the building of freeways. By the 1990s and early 2000s, many of these developments had started to play out as the ratio of male to female drivers reached parity, as baby boomers were reaching late middle age, and as the freeway building boom came to an end. Although the aging of the baby boom cohort and other demographic and socioeconomic changes were predictable, few travel forecasters antici- pated the moderation in travel demand growth that would ensue in the early 2000s. Figure 4-11 shows trends in national VMT and VMT per capita since 1992. For more than a dozen years, VMT per capita has re- mained below its peak in 2003â2004, but total VMT has rebounded since the Great Recession.2 The causes of this plateauing in VMT per capita remain unclear, although the decline in VMT in the late 2000s could be attributable to the Great Recession. 2 Between 2005 and 2015, population grew at about 0.9 percent per year; annualized GDP growth was about 1.72 percent (with negative GDP growth in 2008 and 2009); and VMT rose by a total of 105 billion miles, with growth declining to a maximum of -1.8 percent annually in 2008 and starting to increase again by 2012 (Google n.d.-a, n.d.-b). By 2015, annual growth in VMT was already above 2 percent (FHWA 2015). FIGURE 4-11 Trends in national vehicle-miles traveled (VMT) and VMT per capita, moving 12-month totals, 1990â2017. SOURCE: Polzin (see Appendix C).
CONFRONTING AN UNCERTAIN FUTURE 103 Because travel demand is influenced by many factors, analysts have studied various components of demand to identify those factors that may explain this recent changing pattern of travel. These efforts have been largely unsuccessful, and there remains a great deal of uncertainty in de- mand analyses as to the causes of this development. This uncertainty, in turn, hinders the forecasting of future trends in travel. Thus, even if U.S. population is projected to grow by more than one-third over the next 40 years, how this growth will translate to changes in VMT, and to demand on the Interstate System, remains in question. By way of example, demographers can predict with reasonable confi- dence that the U.S. population as a whole will age over the next 50 years. It is well understood that older people have historically driven less than younger people; they make fewer daily trips, travel shorter distances, and have shorter travel times relative to those under age 65. They also do the bulk of their driving at different times of the day than younger people be- cause they are more likely to be out of the workforce, and thus less likely to contribute to the traffic of peak commuting periods. According to projec- tions, the share of people aged 65 and older will increase from 13 percent of the population to more than 23 percent between 2010 and 2060 (see Figure 4-12) (Chi [see Appendix E]). The number of people aged 65 and older will double, from just more than 40 million to more than 98 million. Notably, the oldest segment of the population, those aged 80 and older, will increase from 11 million in 2010 to 40 million by 2060. However, considerable uncertainty remains as to how this aging population and its travel behavior will continue to affect VMT trends. Studies have shown that increasing FIGURE 4-12 Projected aging population (aged 65 and older) in the United States, 2010â2060. SOURCE: Chi (see Appendix E). 2010 P o p u la ti o n in 1 00 0s 10,000 20,000 40,000 50,000 60,000 80,000 30,000 70,000 90,000 100,000 0% 5% 10% 15% 20% 25% 30% P er ce n ta g e o f T o ta l P o p u la ti o n 2020 2030 2040 2050 2060 80+ 65-79 Percentage of population 0
104 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM numbers of older people hold driverâs licenses and drive. They have grown accustomed to using automobiles for most daily activities, and many live in the suburbs without alternative transportation means available. Even if the elderly do not drive as much themselves, they may still require the con- veniences of the highway system through their use of online and delivery services and shared-vehicle services. Technology also could have a major impact, with fully automated vehicles providing the opportunity for the use of private cars by those lacking driving licenses. Future VMT will be affected not only by demographics but also by changes in GDP; household income; and other economic conditions, such as fuel prices, trade, and economic productivity. While trends in some of these variables can be projected with a reasonable degree of confidence, they collectively add to the uncertainty inherent in forecasting highway travel over many decades. The dynamics of differences in freight inten- sity across industries and the effects of changes in the mix of industries on demand for access to the Interstate Highway System discussed earlier also can affect the amount of truck and commercial travel on the high- way system. Changes in the U.S. role in the global economy with respect to major industries such as mining, manufacturing, and agriculture, for example, could have significant implications for trucking (Polzin [see Ap- pendix C]). Other economic and business developments that could affect highway demand include new technologies that will change the relative competitiveness of rail and truck modes. The same observation applies to business practices, such as widespread adoption of same-day deliveries, that affect logistics strategies. The role of technology and its effects on passenger travel are evolving and remain largely unclear. Email, social media, and smartphones have al- lowed many people to incorporate some elements of telecommuting into their jobs. Technology-aided developments are expanding local transporta- tion options, such as by making public transit easier to navigate because of the availability of real-time information of schedule status and routing options. Yet, while some forecasters have assumed that telecommunications and information technology will decrease the need for highway travel, re- search is showing that their impacts have been mixed (Mokhtarian 2009). Ridership in shared-vehicle services, for instance, has implications for local travel on urban segments of the Interstate System. If these services facilitate pooled trips, they may reduce overall trips on urban Interstates, especially during peak periods. Alternatively, if they draw traffic away from transit and increase the total number of vehicle trips, they may compound peak- period congestion on the urban system. Historically, growth in Interstate demand has not been uniform, but concentrated on the urban system. Figure 4-13 shows the relative role of
CONFRONTING AN UNCERTAIN FUTURE 105 urban and rural Interstates in accommodating national VMT. The trends reveal that urban Interstates have been playing an increasingly important role in accommodating VMT, while the role of rural Interstates has di- minished. Should these trends continue, as appears likely, even modest rates of growth in VMT, measured nationally, may be indicative of dis- proportionately large gains in travel on urban Interstates that will further tax their capacity. The substantial uncertainty about future travel behavior and underly- ing economic, social, and technological conditionsâincluding the prospect of transformational impacts from the introduction of more automated vehicles (discussed later)âfavors a strategy of accommodating various scenarios of future demand. At the national level for the next 20 years, an assumption of annual VMT growth that is roughly equivalent to the Census Bureauâs base forecast rate of population growth (approximately 0.75 percent per year) is reasonable as a low-end estimate (Polzin [see Ap- pendix C]). On the high end, a VMT growth rate about three times greater (on the order of 2 percent per year) would account for an assumption of strong economic growth driving additional travel demand. Sustained VMT growth rates far beyond this range (higher or lower) would be expected only in the face of pronounced changes in the economy (e.g., prolonged contraction or growth periods) or dramatically impactful technology. With regard to the latter, maturation and market penetration of self-driving ve- hicle technologies might suggest very different rates of long-term growth in FIGURE 4-13 Role of urban and rural Interstates in accommodating vehicle-miles traveled. SOURCE: Polzin (see Appendix C).
106 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM VMT. At this point, however, those effects remain altogether unclear, not only in magnitude but also in direction. FUTURE IMPACT OF CONNECTED AND AUTOMATED VEHICLES ON THE INTERSTATE HIGHWAY SYSTEM At a Glance â¢ The development and deployment of connected and automated vehicle technology could have multiple impacts on the future Interstate Highway System, some likely to reduce vehicle-miles traveled (VMT) and some likely to increase it. The magnitude and net direction of these VMT impacts is extremely difficult to estimate, as is their timing. In the case of fully automated vehicles, the societal acceptance of such vehicles is unknown at this time. â¢ A reasonable expectation is that the nationâs highway system will continue to be populated by a mix of vehicles with widely varying levels of automation and human operation for at least the next 20 years. â¢ A 50-year time frame should be adequate to resolve some of the more daunting technological challenges known today to be asso- ciated with connected and automated vehicles. However, so much else in the economy and society could change that translating the deployment of such technologies into forecasts of Interstate demand and supply would be highly speculative. When it was built, the Interstate System was highly innovative, provid- ing faster and safer travel through a range of innovations that included limited access, graded interchanges, cleared roadsides, and medians that separate traffic directionally. From the perspective of a motorist travel- ing on Interstate highways and other freeways today, perhaps the most perceptible change in the system over the past 20 years has been the installation of electronic toll collection and the availability of real-time information on traffic conditions. By reducing backups at toll booths and providing travelers with detour options, these technological innovations have countered some of the highway systemâs congestion problems (TRB 2016). Improvements in work-zone signage, configurations, and protec- tive barriers have made the system safer for highway workers as well as motorists.
CONFRONTING AN UNCERTAIN FUTURE 107 With respect to the driving experience on the Interstates, however, perhaps the most impactful innovations have emerged in the motor vehicle itself. Vehicle innovations now taken for granted, such as reliable radial tires, quiet interiors, and air-conditioning, have made driving more reliable and attractive. During the past 20 years alone, electronic systems provid- ing convenience and safety features have proliferated in the automobile. Smartphones, Internet access, and video players help entertain passengers on longer trips and during traffic delays, potentially making highway travel less onerous. Motorists have less fear of being stranded by mechanical fail- ure because modern cars are significantly more reliable than earlier vehicles, and mobile phones can be used to request help in the event of an emergency. GPS navigation has made driving less stressful on unfamiliar routes and during poor weather conditions. The introduction of other communica- tion, sensing, and onboard electronic systems has helped drivers control their vehiclesâfor example, by taking evasive actions, maintaining safe following distances and lane positioning, and providing blind-side warning (TRB 2016). Collectively, one could make the case that these technological devel- opments have been transformative. Potentially on the verge of widespread introduction, however, are technologies and technological systems that promise even greater change in how people travel and how freight is moved. Notable among these are connected and automated vehicle (CAV) technologies, whose development and deployment could affect the future of the Interstate Highway System. Connected vehicle systems exchange information among vehicles and between vehicles and the roadway infra- structure, while automated vehicle systems may relieve drivers of some, or perhaps all, of the tasks associated with controlling and navigating the vehicle. These technologies are reviewed briefly in Box 4-1 and in depth in Appendix F. Critical to the question of how these systems will affect the future of the Interstate Highway System are their prospective impacts on the demand and supply sides of the system. Demand effects, increasing and decreasing, are expected to include the following (Shladover [see Appendix F]): â¢ Reductions in the need to travel resulting from the opportunity to substitute telecommunications. â¢ Changes in trip scheduling, with better information promoting bet- ter choices for avoiding the worst congestion and safety challenges. â¢ More efficient selection of routes and modes of travel based on better information about viable alternatives.
108 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM â¢ Reduction in the disutility of travel time, thereby encouraging realization of latent demand and potentially inducing new travel demand through locational changes.3 â¢ Improved quality of transit service, encouraging shifts in passenger mode away from personal vehicles and toward transit. â¢ Electronic chauffeuring, providing affordable mobility for travelers who cannot drive, thus encouraging them to travel more than before. 3 âLocational changesâ is a land use planning term that refers to people deciding to move to a home in a different location or businesses deciding to move their offices or shops to a different location. In the context of this chapter, if a long commute trip is not so burdensome, individuals may decide to buy a larger house on a larger plot of land farther away from their workplace. BOX 4-1 Connected and Automated Vehicle Technologies Vehicle-to-vehicle (V2V) connectivity can enable such applications as the following: â¢ Cooperative collision warnings and hazard alerts â¢ Cooperative collision mitigation or avoidance, incorporating active braking â¢ Cooperative adaptive cruise control, with tighter vehicle-following control relative to conventional adaptive cruise control and enhanced traffic flow stability â¢ Close-formation automated platooning, enabling aerodynamic drafting and lane capacity increases â¢ Automated maneuver negotiation at merging locations or intersections â¢ Transit bus connection protection For most of these applications, the communicated data are used to augment the data acquired by onboard remote sensors, which remain the primary source of data on time-critical and safety-critical conditions. Infrastructure-to-vehicle (I2V) connectivity can enable the following: â¢ Providing drivers with traffic signal status information in real time for in- vehicle display, signal violation warning, or green wave speed advisories â¢ Providing drivers with information on traffic and weather conditions and real-time routing advisories â¢ Fleet management functions of vehicle routing and scheduling â¢ Access control to closed facilities â¢ Variable speed limits and advisories provided directly to drivers or their vehicles (I2V cooperative adaptive cruise control) â¢ End of queue warnings â¢ Active support for lane guidance
CONFRONTING AN UNCERTAIN FUTURE 109 â¢ Increased efficiency and improved quality of service by truckingâ potentially including higher-quality, real-time traffic and weather information that enables truck operators to choose better routes, and platooning of trucks that increases the capacity and smooths the traffic on congested truck corridorsâencouraging a freight modal shift toward trucking. CAV technologies could have even greater supply-side effects by pro- ducing changes in multiple aspects of traffic operations that would have effects on safety, travel times, congestion, energy use, emissions, and travel comfort and convenience such as the following: Vehicle-to-infrastructure (V2I) connectivity can enable the following: â¢ Vehicle probe data applications providing detailed traffic information (speed, volume, travel time, queue length, stops) or information on road surface conditions (pavement roughness or slippery conditions) â¢ Mayday and concierge services (such as OnStar) â¢ Electronic toll collection and parking payments â¢ Traffic signal priority requests â¢ Vehicle status information for fleet management (especially for transit and trucking fleets) Automated vehicles are categorized as follows, depending on the level of human engagement in the driving task: â¢ Level 1âThe driver must drive other function and monitor the driving en- vironment. Technologies include adaptive cruise control or lane-keeping assistance. â¢ Level 2âThe driver must monitor the driving environment (the system nags the driver or deactivates itself so as to ensure this). Technologies include adaptive cruise control and lane-keeping assistance, traffic jam assist for freeways, and parking with external supervision. â¢ Level 3âThe driver may read a book, text, or Web surf, but must be pre- pared to intervene when needed. In addition to the technologies in Level 2, the vehicle includes traffic jam pilot technology. â¢ Level 4âThe driver may sleep, and the system can revert to minimum risk condition if needed. Examples of this level of automation include highway driving pilot, closed-campus âdriverlessâ shuttle technology, and âdriver- lessâ valet parking in garages. â¢ Level 5âThe vehicle can operate anywhere, with no driver needed. This level of automation includes ubiquitous automated taxi (even for children) and ubiquitous car-share repositioning systems.
110 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM â¢ Changes in traffic flow stability4 based on differences in vehicle- following dynamics. â¢ Changes in highway lane capacity based on differences in vehicle- following gaps. â¢ Increases in highway bottleneck throughput based on more respon- sive traffic management and the ability to implement situation- dependent speed control. â¢ Reduction in traffic disturbances from lane drops5 and entrance and exit ramp flows through coordinated vehicle merging. â¢ Improved ability to manage incidents based on higher-fidelity in- formation for incident responders, as well as for travelers. â¢ Improved multimodal corridor management in urban areas through enhanced information and control mechanisms. It is apparent that some consequences of CAV deployment will reduce VMT, while others will increase it. If the mobility enhancement effects dominate on the demand side, VMT is likely to increase unless ride shar- ing in automated jitney services becomes the preferred mode of urban and suburban transport, in which case VMT could decrease. The supply-side effects would presumably affect VMT by making highway travel safer and more efficient, but assessing the magnitude of those effects at this stage would be extremely tenuous. Not only is the magnitude of the consequences of CAV deployment difficult to estimate, but its timing is also highly uncertain because of un- knowns regarding the pace of technology advances, the rate of user accep- tance of the technology once it has been developed, and the length of time required to change the vehicle fleet and highway infrastructure. Forecasting the development of information technology is fraught with uncertainty, as this realm is characterized by short-interval cycles of technological change. The life of a generation of integrated circuits is about 18 months, for exam- ple, whereas automotive vehicles are designed and manufactured for service lives of more than a decade, and highway infrastructure requires planning horizons of up to 50 years, and real-world implementation times are likely to be governed by the slowest of the relevant influences (Shladover [see Ap- pendix F]). A serious technological issue that could slow the introduction of CAV technology is the need to ensure sufficient protection against cyber attacks. Providing cybersecurity, already a challenge for contemporary ve- hicle electronics systems, could become far more demanding as attackers 4 In this context, stability refers to desired patterns of density and velocity profiles. 5 Lane drops are defined as locations on a roadway where there is a decrease in the number of lanes for through traffic.
CONFRONTING AN UNCERTAIN FUTURE 111 are tempted to target highly automated vehicles or collections of connected vehicles. A reasonable expectation is that the highway transportation system will continue to be populated by a mix of vehicles with widely varying levels of automation for the foreseeable future, at least for a period of 20 years or more. Manually driven vehicles will continue to be part of the mix, along with vehicles using lower levels of automation to enhance safety and the traveling experience, even after more highly automated vehicles become selectively available for public use. Within 20 years, vehicle connectivity of one type or another is likely to become virtually ubiquitous, providing comprehensive information to travelers and transportation system opera- tors to assist them in making better decisions (Shladover [see Appendix F]). In preparation for this development, the Federal Highway Administration has begun exploring the ways in which the highway infrastructure will need to be adjusted to accommodate these technologies (FHWA 2018b). Recent and ongoing experience with the introduction of advanced vehicle technologies supports a cautious assessment of CAV deployment rates. Figure 4-14 shows how a front-crash prevention feature, automatic emergency braking, has been introduced and taken up in the vehicle fleet. By 2016, 45 percent of new vehicle models offered automated emergency braking as a standard or optional feature, increasing every year from their introduction a decade earlier. However, despite the increasing availability of this feature, only about 5 percent of vehicles on the road were equipped in 2016. The insurance industry estimates that automatic emergency braking systems will not be incorporated in a majority of registered vehicles until somewhere between 2025 and 2030 (see Figure 4-15). An inability to forecast future demand-and-supply side impacts of CAV deployment is problematic for the planning of the future Interstate System, with its many long-lived assets. It will thus be important for trans- portation decision makers contemplating infrastructure investments and mobility needs not to commit themselves to becoming overly dependent on any one expected outcome based on the anticipated availability of a particular technological capability by a specific future date (Shladover [see Appendix F]). A review of the literature by Polzin in Appendix C finds wide-ranging estimates of how the introduction of CAVs will affect future rates of growth in VMT. It supports a conclusion that forecasts of VMT beyond 20 years have limited value for most current decision making purposes. While this conclusion does not imply that large travel impacts from CAVs are unlikely over time, only that the status of technology development and introduc- tion will need to be well monitored to ensure that the timing, direction, and magnitude of impacts are recognized early enough to inform decision making. It will also be necessary to adopt strategies that can accommodate
112 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM FIGURE 4-14 Share of new vehicle models offering automatic emergency braking (top) and registered vehicles equipped with the feature (bottom). SOURCE: HLDI 2018.
CONFRONTING AN UNCERTAIN FUTURE 113 plausible amounts of change and uncertainty, even at the risk of some prep- arations being less than optimal for actual developments in 20 to 50 years. CLIMATE CHANGE AND THE INTERSTATE HIGHWAY SYSTEM At a Glance â¢ Climate change may accelerate the deterioration of Interstate assets, increase operational disruptions, and cause catastrophic failure of some structures. â¢ Decisions will have to be made as to how existing and future Interstate System infrastructure can be made less vulnerable and more resilient to the impacts of climate change, and how changes to the system itself can contribute to mitigating some of the causes of climate change and its impacts. The world has warmed over the past 150 years, a development attribut- able to the rapid increase in carbon dioxide (CO2) and other heat-trapping greenhouse gases (GHGs) in the atmosphere since the industrial revolu- tion of the late 1800s (see literature review in Wuebbles and Jacobs [see Appendix G]). While the amount of CO2 in the Earthâs atmosphere has always been cyclical, its concentration has increased sharply over the past six decades (see Figure 4-16). The Earthâs climate is changing at a pace and FIGURE 4-15 Estimated future percentage of registered vehicles equipped with automatic emergency braking. SOURCE: HLDI 2018.
114 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM in a pattern not explainable by natural influences and many different lines of evidence demonstrate that human emissions of GHGs are largely respon- sible for these changes (Wuebbles and Jacobs [see Appendix G]). A large and looming consideration for decision makers contemplating the future of the Interstate Highway System is how these changes in the Earthâs climate system and associated impacts on temperature, precipita- tion, sea level, and other climate conditions will affect the nationâs transpor- tation infrastructure and how the adverse effects can be mitigated. Given the Interstate Systemâs central role in the overall U.S. transportation system, its future integrity and functioning are especially important considerations. Of particular concern is the strong evidence of an increasing trend in recent decades of certain types of extreme weather events in terms of frequency, intensity, and duration, as well as resulting impacts on societyâ a trend cited as among the most important consequences of a warming climate (Wuebbles and Jacobs [see Appendix G]). Among such extreme weather events are high-temperature and heavy-precipitation events that include more intense and more midlatitude hurricanes and tropical storms, cyclones, and hail and tornadoes associated with thunderstorms. Sea level rise also is closely linked to increasing global temperatures. While uncer- tainty remains as to just how much sea levels will rise during this century, it is virtually certain that they will rise and pose a growing challenge to coastal communities, infrastructure, and ecosystems as a result of such outcomes as increased inundation, more frequent and extreme flooding, and erosion. Existing research indicates that in the coming decades, both the fre- quency and intensity of extreme weather events are likely to increase (Wuebbles and Jacobs [see Appendix G]). Especially relevant outcomes with respect to transportation infrastructure will be increases in intense precipitation events, increased Arctic temperatures (leading to permafrost melting), sea level rise, very hot days and heat waves, and increased hur- ricane intensity. For the Interstate Highway System in particular, climate FIGURE 4-16 Global emissions of carbon dioxide (CO2) from human activity. SOURCE: NASA n.d.
CONFRONTING AN UNCERTAIN FUTURE 115 variability and change may accelerate asset deterioration, cause operational and service disruptions, and contribute to the catastrophic failure of some structures. Notable impacts identified by the U.S. Department of Transpor- tation (U.S. DOT 2014) include the following: â¢ More frequent/severe flooding of underground tunnels and low- lying infrastructure due to more intense precipitation, sea level rise, and storm surge, requiring enhanced drainage and pumping; â¢ Increased frequency and magnitude of storm surges and relative sea level rise, potentially shortening infrastructure life; â¢ Increased thermal expansion of paved surfaces due to higher tem- peratures and increased frequency and duration of heat waves, potentially causing degradation and reduced service life; â¢ Higher maintenance/construction costs for roads and bridges due to increased temperatures and exposure to storm surge; â¢ Asphalt degradation due to higher temperatures and shorter re- placement cycles, leading to limited access, congestion, and higher costs; â¢ Damage to culvert and drainage infrastructure due to changes in precipitation intensity and snow-melt timing; â¢ Decreased driver/operator performance and decision-making skills due to driver fatigue as a result of adverse weather; and â¢ Increased risk of vehicle crashes in severe weather. Changing seasonal precipitation, increased rainfall intensity, and snow and rain transitions also are likely to affect the Interstate Highway Sys- tem in a number of ways, most dramatically through the elevated risk of flooded highways, tunnels, drainage systems, and connected secondary roads (Wuebbles and Jacobs [see Appendix G]). The Interstate Systemâs vulnerability to flood events and mudslides due to long-duration rainfall is demonstrated by five major flooding and mudslide events during the first half of 2017 that shut down segments of the systemâincluding northern (I-80) and southern California (I-880) in January; north central California (I-5) in February; Idaho (I-86) in March; and the central United States, including Missouri (I-44 and I-55) in Mayâfor days or weeks. While all regions may encounter increased flooding impacts from climate change, the Northeast is particularly at risk due to increasing heavy rainfall, while the Pacific Northwest faces increased slope stability challenges, and the upper Midwest is increasingly vulnerable to spring floods from changing climate (see Figure 4-17). Highway agencies will need to prepare for the particular vulnerability of bridges to flooding events (Wuebbles and Jacobs [see Appendix G]). The two most common bridge failure modes are scour, in which bridge
116 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM foundations are compromised because of erosion, and structural failure during single-event floods. The U.S. Environmental Protection Agency (EPA) estimates that approximately 190,000 bridges overall are vulnerable to the effects of climate change, particularly scour (EPA 2015). Although EPA does not provide estimates specifically for the Interstate System, it es- timates that approximately 75 percent of bridges in parts of the Northeast are structurally vulnerable to effects of inland flooding and long-term river flow changes (see Figure 4-18). As noted earlier, sea level rise is a particular concern for highways located in coastal and low-lying areas. By the end of the present century, global sea levels are projected to rise 1 to 4 feet (Wuebbles and Jacobs [see Appendix G]). Because of differences in topography and development patterns, the resulting threat will vary by region and location, with states along the Atlantic and Gulf Coasts expected to experience greater impacts relative to states on the Pacific Coast (see Figure 4-19). Interstate highway infrastructure in the coastal zones is already vulnerable to extreme weather eventsâa vulnerability that will increase with sea level rise, storm surge from more tropical and nontropical storms, and land subsidence. Hur- ricanes Matthew (2016), Sandy (2012), Ike (2008), and Katrina (2005) caused billions of dollars in damage to coastal roadways and bridges, FIGURE 4-17 An on-ramp to Interstate 380 in Cedar Falls, Iowa, flooded as waters rose in 2008. SOURCE: U.S. Air Force 2008.
CONFRONTING AN UNCERTAIN FUTURE 117 including significant economic losses due to transport disruption during and after the storms. Critical Interstate corridors and assetsâsuch as I-95 and I-678 in the New York/New Jersey coastal regionâare susceptible to seawater flooding and inundation. I-64, I-264, and I-564 in Virginiaâs Hampton Roads region are especially vulnerable to rising seas and storm surge. These Virginia highways serve not only a local population of more than 1 million and one of the East Coastâs main ports, but also the nationâs largest naval base and more than two dozen other military bases and sup- port facilities. Likewise, segments along I-10, I-55, and I-59 on the Gulf Coast are considered vulnerable to rising seas and storm surges. The choices being made now and in the next few decades about GHG emissions from fossil fuel and land use changes will influence the extent of additional warming over this century and beyond. As with the effects of CAV deployment, however, climate change impacts and needed adaptations must be considered under conditions of uncertainty. Uncertainties about how the economy will evolve, what types of energy will be used, and how cities, buildings, and vehicles will be designed in the future are among the factors that limit the ability to project changes in climate. Given that mo- tor vehicles account for about 25 percent of U.S. GHG emissions and that about a quarter of VMT is on the Interstates, the future use of the Interstate System will be an important part of this choice set. FIGURE 4-18 Bridges identified as vulnerable in the second half of the 21st century as a result of climate change. SOURCE: Adaptation of Figure 1 in EPA 2015, 34.
118 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM FIGURE 4-19 Regional sea level rise (feet) in 2100 for the United States, projected for the Interagency Intermediate Scenario. Global mean sea level rise is projected to be 1 meter (3.3 feet) by 2100. Much of the eastern and southern United States is projected to experience a larger sea level rise than the global average. SOURCE: Sweet et al. 2017. Travel on the Interstates now accounts for about 7 percent of total U.S. annual GHG emissions.6 How that share will change will depend in part on public-sector initiatives to further the development and use of fuels that produce lower GHG emissions. Some countries, including France, China, and the United Kingdom, as well as some vehicle manufacturers, have an- nounced intentions to phase out vehicles powered by internal combustion; oil companies are investing in charging stations for electric vehicles (EVs) (see Bousso 2017); and some states are embracing electrification through the Zero-Emission Vehicle Memorandum of Understanding (ZEV MOU) (Georgetown Climate Center 2013). Californiaâs ZEV regulation, which also has been adopted by nine other states, requires a minimum percentage 6 Estimate calculated using Interstate VMT values from Highway Statistics 2016 (FHWA 2016), fleet miles per gallon from the Transportation Energy Data Book (edition 36) (Oak Ridge National Laboratory 2018), fuel (gasoline and diesel) CO2 emissions from EPA (EPA 2005), and adjustment to account for GHGs other than CO2 from EPA420-F-05-004 (EPA 2005).
CONFRONTING AN UNCERTAIN FUTURE 119 of sales of zero-emission vehicles, such as battery electric, fuel cell, and plug-in hybrid. The U.S. Energy Information Administration (EIA) proj- ects that sales of battery electric vehicles will likely grow from less than 1 percent of total vehicle sales in 2017 to 12 percent in 2050 (EIA 2018) (see Figure 4-20). As encouraging as these electric power developments may be, they can best be described as necessary but not sufficient to reduce GHG emissions markedly: today, about two-thirds of Americaâs electricity is generated using hydrocarbon fuels (EIA n.d.). It merits noting that the Federal Highway Administration (FHWA), through its Alternative Fuels Corridors program (as required by Congress), in collaboration with the states, is facilitating the deployment of alterna- tive fuels by designating highways that meet specified criteria for charging and fueling infrastructure.7 The stated goal is to ensure that fuel stations offering fast electric charging capability are located no more than 50 miles apart along Interstate routes, are not more than 5 miles from exit ramps, and are accessible to the general public (see Figure 4-21). Through increased access to recharging infrastructure, and in other ways, the future Interstate System may play a complementary role in 7 The Alternative Fuels Corridors program focuses on designating Interstate corridors that already have access to alternative fuels (i.e., electricity, compressed natural gas, liquid natural gas, hydrogen, and propane). This annual designation program, started in 2016, entails cor- ridor nominations from the states and evaluation of the corridors against a set of criteria. If a nominated Interstate corridor meets the criteria, it is designated as an Alternative Fuels Corridor. As of March 2018, more than 80 Interstate Alternative Fuels Corridors had been designated in both urban and rural areas; the designated corridors are located in 44 states plus the District of Columbia. FIGURE 4-20 U.S. sales of battery-powered vehicles. SOURCE: EIA 2018.
120 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM encouraging EV deployment (see Box 4-2). It is even conceivable that in the future, EV recharging will be enabled through the pavement itself, as technologies such as inductive charging (which moves the energy storage from the vehicle battery to the road via charging pads in the road surface or coils embedded in thin strips along the center of a lane) are being piloted in the United States and abroad (Lant 2017). In this regard, the uncertainty faced by decision makers about the future of the Interstate Highway Sys- tem is multifaceted, involving choices about how the infrastructure should be made more resilient to the ongoing and anticipated adverse impacts of climate change, what provisions should be made in near-term highway con- struction to allow for the incorporation of future technology opportunities, and how changes to the Interstate System itself can help mitigate the causes of climate change. SUMMARY Federal and state decision makers planning and making investments in the Interstate Highway System face numerous uncertainties about the systemâs future use and development. The systemâs status over the next several de- cades is likely to be affected by many factors, from the pace and location of the nationâs population and economic growth to potentially transforma- tive changes in technology and in the damaging and disruptive effects of climate change. Uncertainty about the number of influential factors, their FIGURE 4-21 Electric vehicle charging stations near Interstate highways in the Gulf Coast and lower Atlantic states. SOURCES: Alternative Fuel Toolkit website, a product of the Deployment of Al- ternative Vehicle and Fuel Technologies Initiative, a joint project of the Oregon Department of Transportation (DOT) and other state DOTs, along with FHWA (http://altfueltoolkit.org/materials/find-an-alternative-fuel-station).
CONFRONTING AN UNCERTAIN FUTURE 121 interactions, and the potential for each to evolve in various ways creates an environment for decision making that is complex but must be considered when making investments in the Interstate System and other long-lived transportation infrastructure. This chapter has examined the following key factors. Population and economic growth. Some factors that will almost cer- tainly influence the future demand for Interstate highway transportation, as well as the systemâs performance and conditionâparticularly the likelihood of at least moderate population growthâcan be anticipated with a reason- able degree of confidence absent catastrophic events. Continued economic growth can also be reasonably expected over a decades-long period, and these two factors together should lead to increased demand for motor ve- hicle travel in general and on the Interstates in particular. Growth in VMT BOX 4-2 Complementarity of the Interstates to Climate Change Mitigation Initiatives A recent report from the Intergovernmental Panel on Climate Change (IPCC) concludes that global greenhouse gas (GHG) emissions from human activity must be cut nearly in half by 2030 and to a far greater degree by 2050 to slow the rate of global warming (IPCC 2018). The transportation sector is the largest U.S. con- tributor of carbon dioxide and other GHG emissions, and its share of total emis- sions is increasing (EPA 2018). As the backbone of the U.S. transportation sector, the Interstate Highway System contributes to these emissions and can thus play an important role in reducing them. Inasmuch as the Interstate Highway System has facilitated low-density suburban development and reliance on automobiles, a transformation to a low- and no-carbon transportation system will increasingly mean that its planning is integrated with the planning of low-carbon mobility op- tions, from public transit to zero-emission trucks. Many states, counties, and cities are investing in low-carbon transportation solutions, seeking to create new opportunities for both low-carbon mobility and economic development. They are promoting the use of lower-carbon fuels and vehicles, improvements to the operational efficiency of their transportation sys- tems, and alternative transportation modes that do not depend on fossil fuels (U.S. DOT 2010). Currently, 10 states require the sale of zero-emission vehicles (Auto Alliance n.d.), and they and some other jurisdictions are providing incentives for the purchase of electric vehicles (DOE n.d.). Complementary to these policies, states in the Mid-Atlantic and New England are cooperating through the Trans- portation and Climate Initiative to promote electric vehicle corridors and explore regional low-carbon transportation policy options (Bradbury n.d.). Likewise, states in the Rocky Mountain region are collaborating on planning for the deployment of charging infrastructure that is configured to enable electric vehicles to travel long distances without charging gaps (Goetz n.d.; State of Colorado 2017; West Coast Green Highway n.d.).
122 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM on the Interstate System averaging between 0.75 percent and 2 percent an- nually for the next 20 years is a reasonable but admittedly broad planning range, assuming that VMT will largely at least keep pace with projected population growth and possibly increase more rapidly as a result of income and economic expansion. It is reasonable to assume that this added VMT will be concentrated in the countryâs metropolitan areas, which have seen the greatest growth in population and VMT over the past several decades. The geographic and sectoral distribution of the countryâs population gains and economic growth. These factors are also likely to affect the demand for connections to the Interstate Highway System. It is widely expected that most of the countryâs population gainsâand much of the accompanying growth in economic activityâwill follow the pattern of the past several decades by concentrating in states of the South and West and their fast-growing cities and metropolitan regions. Sectoral changes in the economy, including the mix of economic activity across industries that are more or less freight-intensive, are also likely to be factors in the future demand for Interstate highway transportation, but these more granular de- velopments are much more difficult to forecast over longer periods relative to overall trends in population and economic growth. The introduction and widespread deployment of connected and auto- mated vehicles. This potentially revolutionary factor in the future of the Interstate System has implications for both the demand and supply sides of the system. The likelihood of major effects on the system from such deployments over the next two decades appears to be modest because of the need for some still significant technology advances, including safety and cybersecurity assurances; the need to develop and implement protocols and processes for ensuring suitably maintained and equipped infrastructure; and the simple fact that vehicles have become more expensive and durable, lengthening the period of time for turnovers in the vehicle fleet. Beyond a period of 20 or 30 years, and certainly in the decades that follow, the tech- nological changes in this area could be transformative, but in what respect and to what effectsâeven as to whether VMT increases or decreasesâcan only be a matter of speculation at this time, particularly when one is con- sidering a single element of the nationâs transportation system, that is, the Interstate Highway System. Climate change. Climate change poses the very real prospect of dramatic effects on coastal and riverine regions due to sea level rise and flooding; in- creased incidence and severity of extreme and catastrophic weather events; and changes in the norms for weather and environmental conditions that have long been the basis of highway design, construction, and maintenance standards. These developments are likely to have major implications for the future of the Interstate System. Substantial investments will be needed to make the system less vulnerable and more resilient to these effects, starting
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