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From page 85... ... 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. Read the entire page →
From page 86... ... 86 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM economic activity, technology, and other factors -- including the availability of alternatives to highway travel -- could translate into differing rates of growth in motor vehicle travel demand in general and on the Interstate System specifically. • Shladover (see Appendix F) Read the entire page →
From page 87... ... CONFRONTING AN UNCERTAIN FUTURE 87 population, this section also considers how sectoral, compositional, and locational shifts in economic activity among regions could have implications for demand for access to the Interstate System. As discussed in Chapter 3, between 1980 and 2015, vehicle-miles traveled (VMT) Read the entire page →
From page 88... ... 88 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM CHANGING CENTERS OF POPULATION AND ECONOMIC ACTIVITY At a Glance • 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. Read the entire page →
From page 89... ... 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. Read the entire page →
From page 90... ... 90 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM (a) Population Change (b) Read the entire page →
From page 91... ... CONFRONTING AN UNCERTAIN FUTURE 91 access to an Interstate highway (although some of these counties may be located within 20 miles of one) Read the entire page →
From page 92... ... 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) Read the entire page →
From page 93... ... CONFRONTING AN UNCERTAIN FUTURE 93 truck traffic, on average trip distances, and on the origin–destination patterns of that traffic. The core drivers of the U.S. Read the entire page →
From page 94... ... 94 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM specialization in the basic industries can result in even more shifting of the origin–destination 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 Interstate Highway System. Read the entire page →
From page 95... ... 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. Read the entire page →
From page 96... ... 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. Read the entire page →
From page 97... ... CONFRONTING AN UNCERTAIN FUTURE 97 Industry Tonnage (Millions) Tons per Employee % by Truck % by Mult. Read the entire page →
From page 98... ... 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 country's metropolitan areas and megaregions. Read the entire page →
From page 99... ... 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 affected by lower fuel prices. Read the entire page →
From page 100... ... 100 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM FUTURE TRAVEL DEMAND AND THE INTERSTATE SYSTEM At a Glance • Some of the factors that drove vehicle-miles traveled (VMT) during 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. Read the entire page →
From page 101... ... 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 insight into how travel trends will change in the future and affect the use of Interstate highways. Past trends in VMT have been influenced by numerous factors, many of which (e.g., rising income, population growth) Read the entire page →
From page 102... ... 102 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM baby boom cohort reaching adulthood and forming households; and the post–World 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. Read the entire page →
From page 103... ... 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 demand analyses as to the causes of this development. Read the entire page →
From page 104... ... 104 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM numbers of older people hold driver's 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. Read the entire page →
From page 105... ... 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 diminished. Read the entire page →
From page 106... ... 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. Read the entire page →
From page 107... ... 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. Read the entire page →
From page 108... ... 108 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM • Reduction in the disutility of travel time, thereby encouraging realization of latent demand and potentially inducing new travel demand through locational changes.3 • Improved quality of transit service, encouraging shifts in passenger mode away from personal vehicles and toward transit. • Electronic chauffeuring, providing affordable mobility for travelers who cannot drive, thus encouraging them to travel more than before. Read the entire page →
From page 109... ... CONFRONTING AN UNCERTAIN FUTURE 109 • Increased efficiency and improved quality of service by trucking -- 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 corridors -- encouraging a freight modal shift toward trucking. CAV technologies could have even greater supply-side effects by producing 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) Read the entire page →
From page 110... ... 110 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM • Changes in traffic flow stability4 based on differences in vehiclefollowing dynamics. • Changes in highway lane capacity based on differences in vehiclefollowing gaps. Read the entire page →
From page 111... ... 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. Read the entire page →
From page 112... ... 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) Read the entire page →
From page 113... ... CONFRONTING AN UNCERTAIN FUTURE 113 plausible amounts of change and uncertainty, even at the risk of some preparations being less than optimal for actual developments in 20 to 50 years. CLIMATE CHANGE AND THE INTERSTATE HIGHWAY SYSTEM At a Glance • Climate change may accelerate the deterioration of Interstate assets, increase operational disruptions, and cause catastrophic failure of some structures. Read the entire page →
From page 114... ... 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 responsible for these changes (Wuebbles and Jacobs [see Appendix G] Read the entire page →
From page 115... ... 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. Read the entire page →
From page 116... ... 116 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM foundations are compromised because of erosion, and structural failure during single-event floods. Read the entire page →
From page 117... ... CONFRONTING AN UNCERTAIN FUTURE 117 including significant economic losses due to transport disruption during and after the storms. Critical Interstate corridors and assets -- such as I-95 and I-678 in the New York/New Jersey coastal region -- are susceptible to seawater flooding and inundation. Read the entire page →
From page 118... ... 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. Read the entire page →
From page 119... ... CONFRONTING AN UNCERTAIN FUTURE 119 of sales of zero-emission vehicles, such as battery electric, fuel cell, and plug-in hybrid. Read the entire page →
From page 120... ... 120 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM encouraging EV deployment (see Box 4-2) Read the entire page →
From page 121... ... 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. Read the entire page →
From page 122... ... 122 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM on the Interstate System averaging between 0.75 percent and 2 percent annually 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 country's metropolitan areas, which have seen the greatest growth in population and VMT over the past several decades. Read the entire page →
From page 123... ... CONFRONTING AN UNCERTAIN FUTURE 123 soon in cases in which long-lived assets are being planned, sited, constructed, and rebuilt. Projections of climate change and its impacts will need to be translated into new and revised highway design and construction standards well in advance of the time at which these impacts become widely manifest, including for routine repair and rehabilitation projects that collectively represent major areas of Interstate investment. Read the entire page →
From page 125... ... CONFRONTING AN UNCERTAIN FUTURE 125 Sweet, W Read the entire page →

From page 85...

... 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.