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3 Emerging Challenges Having served as the backbone of the countryâs transportation system for more than half a century, the Interstate Highway System is aging and in many places is worn and congested. Nonetheless, it is being counted on to serve as that backbone for decades to come. States face a number of chal- lenges to ensure that it can do so, some that have long been apparent and will almost certainly require near-term attention, and others that are only now becoming evident but have the potential to be even more demanding and transformative in their effects. Critical challenges that have been apparent for many years include the need for a massive renewal of the systemâs deteriorating foundations1 and upgrades to its capacity to accommodate and manage already high traffic volumes that are continuing to grow and shift in location. More than half a century of intensive use has taken a toll on the system. Once a showcase of modernity, the Interstates now contain tens of thousands of miles of pavement that have been subject to age and wear with little more than periodic resurfacing and modest additions to capacityâall in the face of marked increases in use. A backlog of repairs to deteriorated foundations and chronic traffic delays have come to plague the systemâs most heavily traveled urban routes, where demand and capacity are often unmanaged. Although the system has long been considered complete in its national 1 The purpose of pavement and bridge foundations, which consist of the subbase and its associated strengthening materials, is to transfer the loading from the pavement or bridge structure to the soil or subgrade. 49
50 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM and interregional coverage and connectivity, shifts in the geography of the countryâs population and economic activity are creating demands for the addition of new nodes and links, and in some cases for the modification or replacement of urban segments viewed as unduly intrusive to communities. Even as these long-standing but increasingly pressing challenges de- mand attention, new ones are emerging that may prove even more vexing. Continued advances in technologyâranging from more efficient and faster construction methods and more durable materials to electronic tolling and increasingly connected and automated vehicles2âcould make the rebuilding of the Interstate System and the allocation of its capacity more manageable while furthering the continual goal of increasing safety. Rapidly changing technologies, however, could also create new challenges, such as ensuring that the systemâs operations do not become prone to new safety risks and are secure from cyberattacks. Such eventualities will almost certainly take place within the context of a changing climate that will compel transporta- tion agencies to make the Interstate System increasingly resilient to damage and disruptions resulting from rising sea levels and extreme weather events. In addition, there is the imperative to modernize the Interstate Highway System in a manner that contributes to reducing greenhouse gas (GHG) emissions to levels needed to avoid the worst impacts of climate change. While exactly how these developments will evolve over the next several decades remains uncertain, there is little question that they will present significant challenges. The need to rebuild the systemâs foundation and ra- tionalize its capacity is inevitable, as are major changes in technology and climate as the Interstate System moves deeper into the 21st century. This chapter describes these challenges in general terms, while the next chapter considers them in the context of the countryâs changing demographic, eco- nomic, climate, and technological landscape. 2 The term âconnected vehiclesâ refers to vehicles that incorporate technologies that allow them to communicate with other vehicles, facilities, or persons with the same technology. Automated vehicle systems, on the other hand, include technologies that do not rely on com- munication with other entities but relieve drivers of some or all of the tasks associated with controlling the movement of the vehicle.
EMERGING CHALLENGES 51 REBUILDING THE SYSTEMâS FOUNDATION At a Glance â¢ As the foundation of a pavement continues to deteriorate, resurfacing will no longer rectify the damage, and the pave- ment structure will need to be rebuilt from the subbase up. â¢ Most segments of the Interstate Highway System retain their original underlying structure. Thousands of miles are past due for a complete rebuild; thousands more will become due in the next 20 years. â¢ Repeated pavement resurfacing can produce higher life-cycle costs relative to full-depth periodic pavement reconstruction. â¢ Even the newest segments of the Interstate System will need to be rebuilt in the next 20 years. If the entire 49,000-mile system is to be rebuilt over this period, an average of more than 2,400 miles will need to be rebuilt each year. â¢ Today, more than one-third of Interstate bridges have been in service for more than 50 years. They will require investments that will add significantly to the challenge of renewing the systemâs pavement foundation. Most of the miles of highway on the Interstate Highway System are more than 40 years old, and about one-third are more than 50 years old. Nearly all have been resurfaced, often multiple times. In most cases, however, their foundations have not been rebuilt, despite decades of stress from high traffic levels that were largely unanticipated in their designs (Hallin et al. 2007, 9). The condition of a pavement foundation is affected by a variety of factors, including traffic volumes and loadings, construction quality and materials, design details, drainage effectiveness, soil properties, and freezeâ thaw conditions along with the deleterious effects of deicing chemicals (TRB unpublished). When a pavement foundation deteriorates, the effects eventually become manifest at the surface as cracked, rutted, and spalled top layers that must be repaired and resurfaced at shorter intervals to regain smoothness and serviceability. As the foundation continues to deteriorate, surface repairs will no longer rectify the damage, and the pavement struc- ture will need to be rebuilt from the subbase up (see Figure 3-1). The pavements on many of the Interstate Systemâs older segments had reached the end of their design lives before 1980, even as the final planned segments of the system were being built. Now, even the pavements built in the 1980s and early 1990s, at the end of systemâs original construction phase, have reached or will soon reach the end of their design lives. In those
52 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM cases in which Interstate segments have already undergone full reconstruc- tion, the work was typically undertaken for reasons in addition to pavement serviceability, such as to add traffic capacity and safety upgrades. While the number of lane-miles on the system that has undergone full reconstruction is not documented, it is reasonable to conclude that fully rebuilt segments account for only a small percentage of total system lane-miles and that most segments have their original substructure. Accordingly, thousands of miles of Interstate highway are past due for a complete rebuild, and thousands more will become due over the next 20 years. Federal laws and policies, which have emphasized different priori- ties, have contributed to this deferral of reconstruction work. For the first 20 years of the Interstate highway program, federal highway funds, by law, could be used only for new construction and full reconstruc- tion. That policy was changed, however, when the Federal-Aid Highway Act of 1976 authorized states to use federal funds for major repairs and partial reconstructions to keep the deteriorating portions of the highway system serviceable. As a result of this policy change, federal funds could be used for Interstate highway pavement resurfacing and rehabilitation. States welcomed the change because the cost of fully reconstructing dam- aged pavements to new standards had escalated, heavy traffic demands had FIGURE 3-1 Simplified highway cross section. NOTE: For the purposes of this report, the sub-base course and sub-grade and natural soil cross sections are considered components of the foundation as they relate to investment in reconstruction.
EMERGING CHALLENGES 53 complicated the planning and execution of such projects, and the number of highway segments sustaining surface damage had grown steadily as the stressed system aged (TRB 1987, 14â16). States thus devoted most of their federal aid to new construction and surface maintenance, but at the cost of repeatedly deferring the needed replacement of their aging and damaged highway foundations. The circumstances that contributed to this change in federal policy had not been anticipated by the original planners of the Interstate System. When Congress first funded Interstate construction in 1956, it required states to plan and design for the traffic levels expected in 1975 (Smith and Skok 2007). Congress and the states did not anticipate the rapid growth in passenger car and truck traffic that would ensue during the 1960s and 1970s. While the countryâs population grew by 30 percent between 1956 and 1975, total vehicle-miles traveled (VMT) grew by 120 percent.3 By 1975, 19 percent of the countryâs motor vehicle travel was on the Interstate System (FHWA 1975, Table VM-2). Truck travel had increased, and truck loads had grown to be much heavier than anticipated, largely because of changes in state weight limits, but also because of changes in federal policy. The 1956 act that created the Interstates included a single-axle truck weight limit of 18,000 pounds, a tandem-axle weight limit of 32,000 pounds, and a gross vehicle weight (GVW) limit of 73,280 pounds. While these limits were established as a condition for receipt of federal-aid funds, they were also accompanied by a grandfather provision that allowed states with higher weight limits to keep them. Responding to concern that state- to-state variability in weight limits created inefficiencies in the long-haul movement of freight, Congress in 1982 required all states to increase their minimum axle weight limits to 20,000 and 34,000 pounds for single- and tandem-axles, respectively.4 Congress also raised the maximum GVW to 80,000 pounds. Together, increased truck weights and traffic volumes greatly increased loadings on Interstate pavements. This increase is displayed for the coun- tryâs rural Interstates in Figure 3-2 for the period 1970 to 2014. Pavements were deteriorating more rapidly than projected, and states were being pressed to spread their resources across worn segments, favoring faster and less expensive pavement overlays as opposed to more expensive, disruptive, and time-consuming full reconstruction. Box 3-1 summarizes trends in the condition of Interstate pavements as reported in the U.S. Department of Transportationâs (U.S. DOTâs) biennial Conditions and Performance (C&P) report (FHWA 2016c). As noted, stan- dard indicators of pavement condition, consisting of measures of surface 3 Travel statistics in this paragraph are from FHWA (1995, Table VM-201). 4 Surface Transportation Assistance Act of 1982 (Public Law 97-424).
54 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM roughness or smoothness, suggest that states have been improving the con- dition of their Interstate pavement overlays in recent years by judiciously targeting their resurfacing and partial reconstruction work.5 Underlying structural conditions, however, are not generally revealed by measures of surface smoothness and roughness. Studies of highway life-cycle costs that have investigated the practice of repeated pavement resurfacing to re- gain smoothness have confirmed that it produces diminishing returns over timeâthat is, shorter periods of serviceability between successive overlays. These studies have confirmed that this practice can produce higher life-cycle costs than an approach employing full-depth pavement reconstruction that is timed to reduce the frequency and total number of pavement repairs and overlays.6 5 Focused on reconstruction of the pavement surface layers, but not its full depth. 6 Arizona DOTâs âEvaluation of the Cost Benefits of Continuous Pavement Preservation Design Strategies Versus Reconstructionâ (Smith et al. 2005) showed that reconstruction be- comes as cost-effective as continuous preservation (e.g., using thin overlays, micro-surfacing, or other surfacing techniques) after two to three cycles of rehabilitation. FIGURE 3-2 Percentage change in daily traffic volumes and loadings, rural Inter- states, 1970â2014. NOTE: In this chart, load refers to equivalent single-axle load. Average daily load refers to trucks only, and average daily traffic refers to all vehicles. SOURCE: FHWA 2014a, Table TC-202C. 0 100 200 300 400 500 600 700 800 19 70 19 72 19 74 19 76 19 78 19 80 19 82 19 84 19 86 19 88 19 90 19 92 19 94 19 96 19 98 20 00 20 02 20 04 20 06 20 08 20 10 20 12 20 14 PE R C EN TA G E C H A N G E SI N C E 19 70 YEAR Average Daily Load Average Daily Traffic
EMERGING CHALLENGES 55 BOX 3-1 Determining Interstate Pavement Condition Using Surface Condition as a Proxy The standard measure of the surface condition of pavements is the International Roughness Index (IRI), which measures cumulative vertical deflections in the pavement in inches per mile. The 2015 Conditions and Performance (C&P) report (FHWA 2016c) recognizes three categories of pavement quality: good, fair, and poor. Mileage rated good or fair is characterized as âacceptable.â As the charts summarizing these ratings show, the mileage receiving acceptable ratings has been increasing over the past two decades for both rural and urban Interstates. However, urban Interstates have a larger percentage of mileage rated as in poor condition. Ratings based on surface condition measures, moreover, do not reveal the underlying condition of pavements (i.e., including substructure) and may merely reflect state spending that is being programmed largely for surface treatments. (a) (b) SOURCE: FHWA 2017a, Table HM-47A.
56 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM The design life for Interstate pavements constructed in the 1950s and 1960s was 20 years. The fact that many of these pavements are still in ser- vice 50 to 60 years later under much higher traffic loadings and volumes than projected suggests that design and construction procedures from that era were more robust than the design records indicate (Mahoney et al. 2007, 90). Nevertheless, even if one assumes that a pavement structure can last as long as 50 years before requiring full reconstruction, this would im- ply that the older Interstate pavements are already in need of replacement, and that even the newest segments, constructed in the 1980s and 1990s, will have to be rebuilt over the next 20 years. If the entire 49,000-mile system had to be rebuilt over this period, starting with pavements that are 50 to 60 years old, this would mean that an average of more than 2,400 miles would have to be rebuilt each year. While a national inventory of Interstate highway reconstruction plans is not available, there are indications that states are recognizing the need to schedule major reconstruction work on their portions of the Interstate System. Information from Pennsylvania DOT reveals that about 15 percent (~400 miles) of its Interstates were constructed or reconstructed from 1999 to 2018.7 Michigan DOT has scheduled 9 percent of its Interstate miles for reconstruction between 2015 and 2023.8 Other states, such as Iowa (I-80), are planning major reconstruction of portions of their Interstate System (IOWA DOT 2016). One of the case studies in Appendix Iâof I-8 in Impe- rial County, Californiaâdescribes a project to replace nearly 50 miles of deteriorated Interstate pavement surface and foundation with continuously reinforced concrete pavement that is expected to provide a substantially longer service period of up to 70 years. This segment of I-8 is a heavily used mixed urban and rural corridor where traffic disruptions would adversely impact both interurban and freight flows. Accordingly, California decided to construct a long-lived pavement structure that would minimize the need for future reconstruction interventions. California has also been imple- menting reconstruction projects in urban corridors. In 1998, for example, it implemented the Long-Life Rehabilitation Strategies Program to rebuild aging urban highway pavement structures with less cost to the traveling public. A 2004 reconstruction of I-15 in Devore is an example project from the program (Caltrans n.d.). The Devore project involved the reconstruction of 2.8 miles of badly damaged pavements in fewer than 20 days, whereas traditional methods would have required a 10-month road closure. Just as Interstate pavements have aged and sustained higher traffic loadings than anticipated, so, too, have the systemâs many bridges. Today more than one-third of the more than 57,000 Interstate bridges have been in service for more than 50 years (see Figure 3-3). Generally, in contrast 7 Personal communication with Pennsylvania DOT staff. 8 Personal communication with Michigan DOT staff.
EMERGING CHALLENGES 57 with pavements, the long-term deferral of major repair work can have cata- strophic effects on bridges. States have therefore been required to pay close attention to their Interstate bridges as they age and sustain damage from us- age or natural phenomena. About 3 percent of Interstate bridges received a poor rating in the 2015 C&P report (based on 2012 data) (FHWA 2016c), with a slightly higher percentage among bridges on the urban system (see Figure 3-4). Bridges receiving a poor rating are seldom unsafe and are almost always the target of state investments to address their deficiencies. The need to keep Interstate bridges in good condition, however, is relevant to the challenge states face in rebuilding their Intestate pavements. As states make investments to maintain the integrity of their aging Interstate bridges, they also need to ensure that their pavements remain serviceable through investments in both reconstruction and surface repairs. Because so many of the Interstate Systemâs original pavement foun- dations have not been replaced and are past due for reconstruction, a substantial reinvestment for this purpose is necessary. As discussed in the next chapter, uncertainties remain about how complicated and costly this work will be, particularly if growth in traffic accelerates deterioration and adds to the disruption entailed in highway repairs. Urban Interstates are particularly demanding with respect to major reconstruction; however, they are also most likely to experience future growth in Interstate traffic that will exacerbate pavement reconstruction needs. FIGURE 3-3 Percentage of the 57,000 Interstate bridges by age (years), 2017. SOURCE: FHWA 2017d. 35% 48% 9% 8% 50 or more years 25 to 49 years 10 to 25 years less than 10 years
58 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM 41% 56% 3% Rural Interstates Good Fair Poor (a) 43% 53% 3% Urban Interstates Good Fair Poor (b) FIGURE 3-4 Share of (a) approximately 25,000 rural and (b) 32,000 urban Inter- state bridges by condition rating, 2017. NOTE: Because of rounding, data may not sum to 100 percent. SOURCE: FHWA 2017d.
EMERGING CHALLENGES 59 EXPANDING AND MANAGING URBAN SYSTEM CAPACITY At a Glance â¢ Between 1980 and 2015, vehicle-miles traveled on the Interstate Highway System grew by more than 160 percent (compared with a 90 percent increase on all other public roads), while total lane- miles on the system grew by only 25 percent. â¢ Urban lane-miles increased by 115 percent from 1980 to 2015, while travel on these highways increased by more than 230 per- cent, and large metropolitan areas are forecast to experience most of the countryâs population and economic growth. â¢ The trucking industry estimates that congestion on the Interstate System, largely in urban areas, added more than $9 billion to operating costs in 2013. â¢ Urban highway congestion is a particularly complex issue, and alleviating it through physical means, such as lane additions, is an expensive and often impracticable option. Growing Congestion With the Interstate Highway System having reached 92 percent of its current length (in center-line miles) and 82 percent of its current lane-miles more than 35 years ago, the systemâs capacity has demonstrably not kept pace with user demand. Between 1980 and 2015, VMT on the Interstate System grew by more than 160 percent, compared with a 90 percent increase on all other public roads (see Figure 3-5). During this 35-year period of sharp growth in user demand, the total lane-miles on the Interstate System grew by only 25 percent (FHWA 2016b, Table HM-260; 2017c, Table HM-220). Keeping pace with user demand has been especially challenging in urban areas. Lane-miles on the urban Interstate System increased by 115 percent from 1980 to 2015. Over the same period, travel on the system in- creased by more than 230 percent9 as the countryâs urban population grew by more than half, compared with near-zero growth in rural population (U.S. Census Bureau 2016). Although the United States is geographically vast, its population has been concentrating in a relatively small number of large metropolitan areas. Today more than 250 million people out of the nationâs 325 million total population live in metropolitan regions, and the 9 Part of the reason for the growth in urban lane-miles and VMT is that some system seg- ments (about 4,000 miles) that were previously designated as rural have been redesignated as urban as the countryâs metropolitan regions grew in population and land area.
60 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM largest 75 regionsâeach having more than 500,000 peopleâaccount for about half the U.S. population (Frey 2016). The Interstates themselves have contributed to the countryâs metropoli- tan growth, making the system increasingly vital to commuting and other local and intraurban travel. In 1980 the urban Interstate System accounted for about 19 percent of all urban VMT; in 2015, it accounted for 25 per- cent (FHWA 2016a, Table VM-202). Moreover, the Interstates have con- tributed to the growth of âmegaregions,â as long stretches of the Interstate System now have a high proportion of urban miles that connect multiple metropolitan regions, such as in the Northeast Corridor (Portland, Maine, to Richmond, Virginia), Texas Triangle (Dallas, Houston, San Antonio), and Southern California (Los Angeles to San Diego counties) conurbations (Georgia Tech Research Cooperation 2008). During periods of heavy local demand, large portions of the urban In- terstate System, both within and outside central cities, fail to accommodate the demand of local as well as interregional and longer-distance travelers. Recurrent episodic congestion resulting from crashes, construction activ- ity, and weather events produces chronic problems on many segments of the urban system during both commuting and noncommuting periods. Researchers at the Texas A&M Transportation Institute (TTI) and INRIX found that, in 2014, one in four urban highway trips were subject to delays FIGURE 3-5 Growth in vehicle-miles traveled on Interstate highways and all other public roads, 1980â2015. SOURCE: FHWA 2016a, Table VM-202. 2,500 V eh ic le -m ile s tr av el ed ( b ill io n ) Rural Interstates Urban Interstates All Interstates All Other Roads 2,000 1,500 1,000 500 0
EMERGING CHALLENGES 61 from congestion and that drivers spent an average of 30 percent more time in their vehicles when traveling during congested compared with noncon- gested periods (Schrank et al. 2015, 8, 10). Although the TTIâINRIX data cover all urban highway trips, the large portion (25 percent) of urban VMT that occurs on the Interstates suggests that these highways are the site of much of this costly delay. Trucks traveling on Interstates when hauling freight long distances are particularly affected by recurrent congestion on urban segments (BTS 2017). Average truck speeds on urban Interstates in some of the countryâs largest metropolitan areas (and over much of the 600-mile I-95 corridor between Richmond, Virginia, and the MassachusettsâNew Hampshire bor- der) are less than 45 mph (see Figure 3-6). Federal Highway Administration (FHWA) data indicate that 49 of the top 50 truck bottlenecks in the country are located at Interstate interchanges in metropolitan areas (ATRI 2017). The trucking industryâwhich is the largest component of the multimodal freight system in the United States, accounting for 65 percent of shipment valueâestimates that congestion on the Interstate System added more than $9 billion to its operational costs in 2013 (ATRI 2014). Urban freeway congestion is a complex issue, and alleviating it through physical means, such as lane additions, is an expensive and sometimes im- practicable option when system right-of-way is constrained by land avail- ability. Even if land can be acquired or existing right-of-way can be used more intensively, urban areas are expensive construction environments, and proposals for capacity expansion are often met with concern and outright opposition because of environmental and community impacts (Polzin [see Appendix C]). Some opponents believe that adding more urban freeway capacity will further contribute to the outward expansion of metropolitan areas, increasing public demand for still more roads and infrastructure (Milam et al. 2017; TRB 1995). Some also contend that expanding capacity by widening existing routes or building new lanes induces additional travel, leading to increased highway VMT adding to congestion over time, as well GHG emissions (Handy and Boarnet 2014). Capacity expansion plans, therefore, may be pursued through a combination of physical expansion and efforts to manage demand. Managing Demand with Operations and Mobility Enhancements Several case studies conducted for this report (see Table 3-1 and Appendix I) illustrate the limited ability to expand congested urban Interstates and the need to couple any possible capacity additions with demand management. Operational strategies to manage demand include variable speed limits, lane control signals, and dynamic conversion of paved shoulders to travel lanes. Corridor-level mobility management programs also coordinate the operation
62 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM of parallel roads and area transit services to reduce corridor congestion and increase overall throughput (U.S. DOT n.d.). On I-25 in Denver and on I-15 in San Diego, for example, the highway agencies and metropolitan planning organizations (MPOs) opted for operational strategies that manage capacity and demand to produce more efficient traffic flows. U.S. DOT is providing guidance to highway agencies interested in implementing integrated, corridor-level mobility management programs. These mobility management programs coordinate the operation of parallel roads and area transit services to reduce corridor congestion and increase overall throughput (U.S. DOT n.d.). Federally supported research has led to advances in tools for transportation system management and operations that promise even more effective corridor management in the future (see, for example, FHWA n.d.-b). Virginia DOT has implemented many of the active traffic management (ATM) features noted above on I-66 outside Washington, DC, in 2015. Previously, this corridor already had time-of-day (during peak periods) hard shoulder running in place, and thus the new ATM was aimed at improving off-peak performance. Its planner estimates that travel times on the corridor have decreased by 4 to 10 percent during FIGURE 3-6 Average truck speeds on Interstates in 2014. NOTE: Speed and travel-time reliability were measured for more than 500,000 trucks on 25 freight-significant corridors on an annual basis (BTS 2015). SOURCE: BTS 2015.
EMERGING CHALLENGES 63 off-peak periods and that delay-causing crashes have declined by more than 25 percent.10 Recently, Connecticut DOT started a bus rapid transit line that runs along I-84 as a means of reducing congestion on the general- purpose lanes (TRB 2016). This example, like the Northern Virginia and Seattle cases in Table 3-1, demonstrates that the Interstate System intercon- nects with local transportation networks and can serve both low-occupancy automobiles and high-occupancy buses. Managing Demand with Pricing Highly congested metropolitan regions are starting to implement congestion pricing on their Interstates (see Box 3-2). However, while the imposition of tolls is allowed on some portions of the Interstate System, including 10 Information in this section relevant to Virginia is based on material presented to the com- mittee by Michael Fontaine (Virginia DOT) in July 2017. TABLE 3-1 Selected Case Studies of Projects Involving Urban Corridors and Interurban Freight Corridors Projects/Plans Improvement Types Smart I-25 Managed Motorways, Denver, Colorado Intelligent transportation systems I-15 Integrated Corridor Management, San Diego, California Integrated corridor management, intelligent transportation systems I-66 Outside Beltway, Northern Virginia Managed lanes, enhanced travel mode choices (bus and rail transit integration, park-and- ride lots), shoulder use, reconstruction of roadways and interchanges I-405 Seattle, Washington Managed lanes, high-occupancy vehicle (HOV) lane conversion, interchange enhancements, peak-period shoulder use, enhanced bus and bus rapid transit (BRT) service I-80 and I-29, Council Bluffs, Iowa Lane additions and interchange improvements to construct three express lanes for I-80 traffic and two local lanes for I-80/I-29 traffic I-590 Winton Interchange, Rochester, New York Interchange reconstruction to diverging diamond* to improve level of service I-85 Kia Boulevard Interchange, West Point, Troup County, Georgia New interchange to improve access to a manufacturing facility, accelerated bridge construction *Diverging diamond is a type of interchange that eliminates the need for leftturning vehicles to cross the paths of incoming vehicles SOURCE: FHWA 2014b.
64 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM some special purpose lanes and highways that were tolled turnpikes before the system was created in 1956, it is prohibited on the large majority of Interstates constructed with federal aid thereafter. This management tool is therefore not available to mitigate congestion on most general-purpose Interstate lane-miles.11 Pricing is limited to deployments on existing high- occupancy vehicle (HOV) lanes and newly constructed lanes that are paid for without federal aid by states and localities, sometimes in partnership with private investors. California has about 250 miles of high-occupancy toll (HOT) lanes in operation and 58 miles of these lanes under construc- tion. Virginia recently opened HOT lanes on I-95 and I-495 outside Wash- ington, DC, and on I-66 inside the I-495 Beltway. The state also plans 11 General-purpose or general-use lanes refer to all lanes that are not express lanes, tolled, high-occupancy vehicle (HOV) lanes, or high-occupancy tolled (HOT) lanes. BOX 3-2 Congestion Pricing The concept of charging tolls that vary with roadway congestion levels has a long lineage, but its application on U.S. highways is fairly recent (TRB 1994). In brief, charging a fee for use of roads during congested periods allocates available sup- ply with demand in the most economically efficient way. Shortages occur when- ever a valued commodity or service has more demand than supply. For industries with high fixed or capital costs, expanding supply often cannot be accomplished in the short run. In the interim, prices rise until supply and demand equilibrate. Goods and services are allocated throughout the U.S. economy using prices to match demand with supply. Variations on congestion pricing, also referred to as value pricing or man- aged lanes, have been applied on U.S. highways for almost two decades, includ- ing on several urban Interstates, with positive results (FHWA n.d.-d). Drivers who pay the toll save time and the revenues earned are available to improve capacity. Drivers faced with fees imposed during congested periods have choices beyond paying the fee, including changing the timing of trips to travel at less congestion times, traveling on routes without fees, sharing rides, or switching to transit. On the Interstates, only new added lanes can be tolled, which means that motorists always have the choice to travel in the unpriced lanes. Equity concerns are typi- cally addressed by exempting vehicles with two or three occupants and transit vehicles from the congestion toll and by using the revenues gained to pay for the expanded capacity and additional transit services in the corridor. In the case of Interstate highways in urbanized areas, land constraints, capital costs, envi- ronmental concerns, and community opposition limit the amount of capacity that can be added. Charging fees during congested periods provides an effective and efficient mechanism for allocating available demand.
EMERGING CHALLENGES 65 to add variable-toll facilities on I-66 outside the Beltway and on I-64 in Hampton Roads. Two planned HOT-lane projectsâI-66 outside the Beltway in Northern Virginia and the I-405 express toll lanes in Seattleâare analyzed as case studies in this report (see Table 3-1 and Appendix I). The combined use of the general-purpose and toll-managed lanes is projected to increase vehicle throughput in the two corridors by 33 percent and 73 percent, respectively. In the case of I-66, the managed lanes are expected to attract some travel- ers who previously used the general-purpose lanes through the provision of toll-free incentives for HOV and bus transit options; accordingly, the cor- ridor is projected to carry 43 percent more travelers relative to the current corridor configuration.12 Similarly, the creation of the new managed lanes along I-820 and I-635 in Texas resulted in an increase of traffic throughput along those corridors.13 By 2016, for example, the general-purpose lanes along the I-820 were carrying between 7 and 10 percent more vehicles than before the managed lanes were constructed. Even with those increases, the average speed in the general-purpose lanes increased between 10 and 15 percent. Whereas free-flowing traffic was guaranteed in the managed lanes, congestion in the general-purpose lanes was also reduced by 60 to 70 per- cent.14 Benefits for passengers in the general-purpose lanes, however, may be temporary as demand continues to grow. The demand for additional physical capacity and for more active and innovative management of new and existing capacity is almost certain to grow as metropolitan areas continue to experience most of the countryâs population and economic growth. As discussed in the next chapter, there is uncertainty about how this anticipated growth will translate to higher pas- senger car and truck traffic volumes. However, this uncertainty centers on the magnitude of the volume increases, not their location, which is expected to be mainly on the urban system. The case studies discussed herein indicate that while large metropolitan regions may continue to pursue the option of constructing new tolled facilities, physical constraints on right-of-way could eventually limit the applicability of this option. Moreover, in large metropolitan regions with widespread system congestion, it may become necessary to implement pricing on Interstates more extensively to incentiv- ize the use of alternative routes and transportation modes and to shift more traffic to off-peak times. Indeed, as discussed in one of the case studies in Appendix I, planning is under way in the San Francisco Bay area to develop 12 Information in this section relevant to Virginia is based on material presented to the com- mittee by Michael Fontaine (Virginia DOT) on July 2017. 13 Information in this section relevant to NTE TEXPRESS and LBJ TEXPRESS is based on material presented to the committee by Belen Marcos on February 2017. 14 Defined by operator as speeds below 50 miles per hour.
66 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM a 550-mile network of toll-managed lanes (Interstate and non-Interstate). The Metropolitan Transportation Commission (MTC) will operate 270 miles of the 550-mile network through conversion of 150 miles of existing carpool lanes and the addition of 120 miles of new lanes. DEMAND FOR CHANGING THE SYSTEMâS LENGTH AND LAYOUT At a Glance â¢ New travel demand arising from economic and population growth in certain areas may warrant changes to the Interstate Highway Systemâs overall length and scope of coverage. â¢ Today, as a result of southern and westward development, more than 37 urbanized areas with populations exceeding 50,000 lack nearby access to Interstate highways. â¢ Ensuring that the Interstate System is responsive to changing user demands will require making choices, particularly regarding the envisioned role of the system for such purposes as international trade; inter- and intraregional traffic; and local, regional, and national economic development. As discussed in Chapter 2, one of the principal planning criteria for the original Interstate Highway System was to connect most U.S. cities with 50,000 or more people (Eisenhower 1955). When the system was being planned in the 1940s and 1950s, waterways and railroads were the pri- mary transportation connectors for the countryâs population and economic centers. Indeed, a comparison of the Interstate map developed in the 1940s and 1950s with a map of the countryâs major railroad trunk lines during the 19th and 20th centuries reveals considerable overlap. Since its advent, however, the Interstate System has both reinforced this earlier pattern of U.S. development and helped realign it toward increas- ingly urban western and southern states. Many of these âSun Beltâ cities have experienced their greatest population and commercial growth since the development of the Interstate System. Some southern and western cit- ies that were not connected to the Interstate System, being relatively small population centers such as Las Vegas and Phoenix, are now some of the countryâs largest and fastest-growing metropolitan complexes. Located far from navigable waters and railroad hubs, they emerged and developed almost entirely after the introduction of the automobile and the Interstate Highway System (TRB 2016).
EMERGING CHALLENGES 67 Although the development of the Sun Belt was in its infancy in the middle of the 20th century, it would have been difficult for the original Interstate System planners to have imagined its speed and scale. Figure 3-7 shows the areas of the country, largely in the South and West, that have experienced the largest population gains over the past three decades (Sieber and Weisbrod [see Appendix D]). Because of this uneven development, in 2017 more than 40 urbanized areas with populations exceeding 50,000 did not have an Interstate highway within 25 miles (see Table 3-2).15 Nearly half of these cities were in California and Texas, and most of the remainder were in other states of the South and West. The scope of the Interstate System is not static, although an argument can be made that its extensions have been added in a mostly piecemeal fashion without strategic guidance. As of late 2018, FHWAâs most recent records show that some of the cities listed in Table 3-2 are now being 15 The 25-mile distance is measured from the Census-defined boundary of the urbanized area to the nearest Interstate route. FIGURE 3-7 Population growth by county, 1985â2015 (dashed lines delineate existing and emerging megaregions). SOURCE: Sieber and Weisbrod (see Appendix D).
68 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM TABLE 3-2 Urbanized Areas (>50,000 population) Farther Than 25 Miles from an Interstate Highway in 2017 City Population McAllen, TX* 728,825 Fresno, CA 654,628 Oxnard, CA 367,260 Santa Rosa, CA 308,231 Atlantic City, NJ 248,402 Visalia, CA 219,454 Brownsville, TX* 217,585 Myrtle BeachâSocastee, SCâNC 215,304 Santa Barbara, CA 195,861 Salinas, CA 184,809 College StationâBryan, TX 171,345 Panama City, FL 143,280 Merced, CA 136,969 Harlingen, TX* 135,663 Santa Maria, CA 130,447 Greenville, NC 117,798 SeasideâMonterey, CA 114,237 Salisbury, MDâDE 98,081 San Angelo, TX* 92,984 Bend, OR 83,794 Madera, CA 78,413 Florence, AL 77,074 Lake JacksonâAngleton, TX 74,830 Oshkosh, WI* 74,495 Porterville, CA 70,272 Dothan, AL 68,781 Dubuque, IAâIL 67,818 Jonesboro, AR* 65,419 El Paso de Robles (Paso Robles)âAtascadero, CA 65,088 Victoria, TX 63,683 Kokomo, IN 62,182 Sherman, TX 61,900 SebringâAvon Park, FL 61,625 San Luis Obispo, CA 59,219 Lexington ParkâCaliforniaâChesapeake Ranch Estates, MD 58,875 Mankato, MN 57,584 Kahului, HI 55,934 Fond du Lac, WI* 54,901 Farmington, NM 53,049 Arroyo GrandeâGrover Beach, CA 52,000 Lewiston, IDâWA 51,924 Lompoc, CA 51,509 Villas, NJ 51,291 New Bern, NC 50,503 *By late 2018 these urbanized areas are located within 25 miles of an Interstate highway.
EMERGING CHALLENGES 69 connected to the Interstate System (FHWA n.d.-c). For example, the addi- tion of I-41 in Wisconsin connected Oshkosh and Fond du Lac, while the addition of I-555 in Arkansas connected Jonesboro. In south Texas, new Interstate construction along the emerging I-69 trade corridor will fully connect three more unserved cities, Brownsville, Harlingen, and McAllen. Although thousands of miles of other, often high-quality, highways (largely on the 225,000-mile National Highway System) also help connect the countryâs population centers, the lack of access to the Interstate System is viewed by some of these smaller and emerging cities listed in Table 3-2 as detrimental to their growth and development. Of particular concern is that the Interstate System comprises the countryâs main trucking corridors, and their users depend increasingly on finely tuned logistics systems that manage freight flows precisely. The Interstate Systemâs role in spawning and shaping the economic growth of newly emerging cities after World War II is not lost on communities that are now challenging the rationale for the systemâs being treated as âcompleteâ when the country it serves is dynamic and changing. In addition to connecting the countryâs population centers for personal travel, the original planners of the Interstate System sought to improve its long-distance freight corridors. The extent to which this planning took into account the freight demands of international trade is unclear, but it was probably minimal given that the annual value of imported and exported goods did not even surpass $50 billion (9.2 percent of gross national prod- uct [GNP] in 1960) until after 1960 (Bureau of Economic Analysis 2018; The World Bank n.d.). Nevertheless, the systemâs original plan containing multiple eastâwest routes was farsighted. It strengthened the position of several West Coast ports (e.g., Long BeachâLos Angeles, Oakland, Seattle, and Tacoma) as they competed for the escalating trade with Japan, Korea, China, and other Pacific Rim countries commencing in the 1960s. It was not until 1979, however, that the final section of the northâsouth I-5 was completed to form the first continuous northâsouth freeway connecting with both Canada and Mexico, which would soon become the United Statesâ largest trading partners. By the time the I-5 corridor was completed, the value of international trade had grown to nearly 5 times that in 1960 when adjusted for inflation (U.S. Census Bureau 2018), and trade with Canada and Mexico was leading the way. The CanadaâU.S. Free Trade Agreement in 1987 and the North American Free Trade Agreement (NAFTA) that included Mexico in 1994 reinforced and then escalated this northâsouth pattern. Today, Canada and Mexico collectively account for nearly 25 percent of the value of U.S. international trade (U.S. Census Bureau 2017). Even before passage of NAFTA, Congress in the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 identified 14 potential future
70 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM freight corridorsâknown as the Congressional High-Priority Corridorsâ whose highways would be upgraded and designated as part of the Interstate System. The CANAMEX Trade Corridor was prescribed to create an Inter- state route parallel to I-5 farther to the east (I-15 spanning from San Diego County, California, to Alberta, Canada). While I-15 has been completed, another northâsouth trade corridor, I-69, is envisioned farther to the east, spanning from Sarnia, Ontario, Canada, to the Lower Rio Grande Valley in Texas. I-69âs development from myriad state highway routes has been delayed by many factors, including the lack of dedicated funding. Keeping pace with the changing levels and patterns of international trade is of course only one source of demand for changes to the length and layout of the Interstate Highway System. Congress has amended its list of high- priority Interstate corridors several times since 1991. As shown in Figure 3-8, the list now includes an eastâwest corridor from Virginia to Kansas and a northâsouth corridor from South Carolina to Michigan. In addition, the list includes some extensions that are intended to bridge system discontinuities FIGURE 3-8 High-priority corridors designated as future interstates by Congress, 2017. NOTES: Colors are added for clarity only. Corridor numbers correspond to statutory listing in Section 1105(c) of ISTEA 1991, as amended. Some portions of the future Interstate have been constructed to Interstate standards, open to traffic, and signed as Interstates. Corridors based on information available as of October 11, 2017. SOURCE: FHWA n.d.-a.
EMERGING CHALLENGES 71 within a single state or across two or three states. These additions are in- tended to serve such purposes as connecting the core cities of expanding megaregions (e.g., RaleighâNorfolk corridor), providing farm-to-market ac- cess (Bakersfield to Sacramento), and supporting interregional and rural economic development (along the route from Memphis to Birmingham). As explained in Chapter 2, under current law FHWA can at the request of a state or states designate sections of the 225,000-mile National High- way System to be absorbed into the Interstate Highway System, but this authority is not accompanied by additional federal funding for the needed upgrades. States must use existing sources of revenue that already are sub- ject to competing demands elsewhere on their systems. The required invest- ment can be substantial. A planned 8-mile upgrade of US-77 to become part of I-69 in Texas (see Appendix I) is projected to cost more than $9 million per mile. The upgrades would include geometric improvements, interchange additions, and pavement reconstructions, all intended to increase capacity and enhance safety. The project to convert US-77 to I-69, which was designated a High- Priority Corridor, is expected to serve multiple purposes, including pro- viding new connections for freight flows between the Rio Grande Valley and the MichiganâCanadian border. This would facilitate the multimodal integration of freight movements by truck, rail, air, and inland waterways at Memphis and improve the connectivity of communities in western Ten- nessee. The project is an example of the effort to ensure that the Interstate System meets changing demands for purposes ranging from facilitating international trade and interregional traffic flows to supporting local and regional economic development. However, it is also an example of how cri- teria have not been established for prioritizing these purposes, particularly to guide the allocation of federal aid. ENSURING SAFETY WHILE ACCOMMODATING A GROWING AND CHANGING VEHICLE FLEET At a Glance â¢ Although the Interstates are the countryâs safest highways, they account for more than 5,000 traffic deaths annually. â¢ Safety assurance will remain a challenge for highway agencies as advanced vehicles and systems affect traffic flows and require infrastructure accommodations. â¢ A critical factor in the safety assurance challenge will be to pro- vide protection from cyberattacks.
72 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Although they are the safest highways per unit distance of travel, U.S. DOT statistics show that more than 5,000 people, representing about 13 percent of total traffic deaths, died in motor vehicle crashes on Interstate highways in 2016 (see Figure 3-9). It has also been noted that Interstate truck traffic has grown much faster than originally forecast, and many of the deaths (21 percent) involve crashes with large trucks. Most of these deaths (72 percent)16 occur in smaller, passenger vehicles that share the road with large trucks. Interstate pedestrian fatalities (472 of 674 in 2016) occur primarily on the urban system where highways cross densely populated areas.17 These fatalities do not include those that occurred on other roads merging with Interstates at interchanges. Despite the safe design of the Interstates relative to other highways, reducing the number of crashes on the system clearly remains an impor- tant challenge. Interstates of the future will need to continue to adopt state-of-the-art safety practices to mitigate the risks arising from growth in traffic volumes and the higher travel speeds permitted. Moreover, changes to accommodate increased traffic demand will need to be accompanied by assessments of the likely safety impacts of those changes and the need to deploy countermeasuresâfor instance, under circumstances in which 16 Analysis provided by the Insurance Institute for Highway Safety, based on data from the U.S. DOTâs Fatality Analysis Reporting System (FARS). 17 Analysis provided by the Insurance Institute for Highway Safety, based on data from FARS. Also, additional research has found a two-to-one ratio between pedestrian deaths on Interstates in urban and rural contexts from 1993 through 2012 (AAA Foundation for Traffic Safety 2014). FIGURE 3-9 Persons fatally injured in motor vehicle crashes, by road classification and as percentage of yearâs total fatalities, 2016. SOURCE: FHWA 2017b, Table FI-220. 0 Interstate Other 13% 5% freeways and expressways Other principal arterial Minor arterial Major collector Minor collector Local P er so n s fa ta lly in ju re d in m o to r ve h ic le c ra sh es 2,000 4,000 6,000 8,000 10,000 12,000 29% 19% 14% 4% 11%
EMERGING CHALLENGES 73 shoulders are repurposed as travel lanes or trucks are allowed to platoon using electronic systems. Many new highway and vehicle technologies being developed and starting to be introduced have the potential to alter the operations and safety performance of the highway system, including Interstates. Many of these technologies are vehicle-centered, such as driving-assist features and automated vehicles, while others, such as real-time traffic analysis systems that regulate traffic control devices, have a strong infrastructure orienta- tion. Still other technologies are aimed at integrating vehicles and highways through increased connectivity (i.e., vehicle-to-vehicle [V2V] and vehicle- to-infrastructure [V2I] communications). Although these features are expected to improve safety and operability, their introduction also poses challenges. In particular, for them to achieve their promise, they will have to function reliably and safely. Designing these new systems to ensure that they are reliable and minimize their potential to introduce unintended safety hazards will be an ongoing challenge for automakers, their suppliers, and highway engineers. Safety assurance will become a special challenge for highway agencies, as advanced vehicles and systems will affect traffic flows, both on and off the Interstates, and likely will require infrastructure accommodations to support some of their capabilities. Although there has been much publicity about the future of automated vehicles, moreover, most vehicles on the road over the next two decades will continue to have human drivers. Mixed fleets of automated and human-operated vehicles will pose a particular challenge. The safety assurance challenge will also demand protection from cy- berattacks, as the advanced electronic, computer, and telecommunications systems of automated vehicles will have the capability to gather, analyze, and transmit large amounts of data that may present opportunities for such attacks by individuals as well as adversarial nations. To address this issue, the automotive industry is assessing cybersecurity risks associated with emerging technologies and working through collaborative organiza- tions, such as the Automotive Information Share and Analysis Center (Auto-ISAC), to develop and share best practices for securing vehicle communications (Auto-ISAC 2018). Likewise, the National Highway Traf- fic Safety Administration (NHTSA) has been working with the National Institute of Standards and Technology (NIST), using NISTâs Technology Cybersecurity Framework (NIST n.d.), to encourage the automotive in- dustry to adopt practices that will improve the cybersecurity of vehicles (NHTSA n.d.). And while neither the existing highway design standards nor the Technology Cybersecurity Framework employed by NHTSA ad- dresses the cybersecure deployment of infrastructure-related technologies,
74 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM the prospect of connected vehicle technologies18 on Interstates and other highways suggests the need for highway agencies to play a far more promi- nent role in such efforts. The development of automated and connected vehicle technologies and their deployment on the Interstate Highway System is a complex topic involving many potential technologies, systems, and capabilities. The com- mittee commissioned a paper (see Appendix F) to provide an overview of the state of technology; its progress; and assessments of how new tech- nologies could impact Interstate highway operations over the next 10, 20, and 50 years. This assessment and related observations by the committee, discussed in the next chapter, suggest that the impacts could be far-reaching and extend over a time horizon that cannot be well defined at this point in time. The challenge for decision makers contemplating the future of the Interstate Highway System will be to ensure that the system is robust and adaptable, avoiding premature investments in assets or the introduction of standards that hinder or foreclose development pathways. ADDING RESILIENCE At a Glance â¢ The potential impacts of changing climate and extreme weather events on the Interstate Highway System are serious and multifold. â¢ Designing and retrofitting Interstate infrastructure to add resil- ience will involve costly undertakings that will require a strategic, risk-based approach. â¢ States need to identify the climate change impacts relevant to their system, how those impacts are likely to manifest, and which system segments are most vulnerable. When much of the Interstate Highway System was being planned, designed, and built during the 1960s and 1970s, there was no understanding of the threat of GHG buildup and how a changing climate could adversely affect the transportation system and other critical infrastructure through such consequences as rising sea levels and extreme weather events. Individual portions of the Interstate System were designed and built for the typi- cal range of weather and climate experienced regionally in the past. For 18 Automated vehicle technologies relieve drivers of some, or perhaps all, of the tasks associ- ated with controlling and navigating the vehicle. Connected vehicle technologies are devices installed in vehicles that exchange information with other devices within the same vehicle, other vehicles, or road infrastructure.
EMERGING CHALLENGES 75 instance, environmental factors such as the expected duration and intensity of rainfall affected design choices about subsurfaces, materials, and drain- age capacity, choices that usually accounted for environmental extremes experienced in the past, such as 100-year storms and floods. The need to make the Interstate System and other transportation as- sets more resilient to the consequences of climate change is now widely recognized, in part because of recent experience and in part because of fore- casts by much of the science community. Increases in very hot days, in the frequency and intensity of precipitation events, and in hurricane intensity, which are predicted effects of climate change, are now being observed.19 In Alaska, for instance, the thawing permafrost is causing subsidence to roadbed and bridge supports. The city of Houston has experienced three 500-year storms since 2015, including Hurricane Harvey, which caused more than $125 billion in damage in 2017 (NOAA 2018). And in 2012, Superstorm Sandy severely affected New York City, the coast of New Jer- sey, and other points along the northeastern seaboard, causing more than $70 billion in damage. According to data from the National Oceanic and Atmospheric Administration, since 1980 the United States has sustained more than 200 weather and climate disasters in which damage, response, and cleanup cost exceeded $1 billion per event (see Figure 3-10). The to- tal cost of these occurrences was more than $1 trillion. Every U.S. state was affected by one or more of these catastrophic events, which included major heat waves, severe storms, tornadoes, droughts, floods, hurricanes, and wildfires. Table 3-3 lists Interstate highways that were recently closed because of severe weather events. The potential impacts of changing climate and extreme weather on the highway system are multifold. Pavements and bridges can be adversely affected not only by extreme changes but also by unexpected deviations from normal weather patterns, such as wetter winters and drier summers. The effects can be pernicious, including the erosion of road base and bridge supports from gradual land subsidence; softening, rutting, and buckling of pavement from excessive heat; and freezeâthaw cycles and thermal expan- sion that damage bridge and pavement joints and decks. Generally wetter conditions, for instance, can reduce the load capacity of pavement structure and require improved surface and subsurface drainage. The extreme effects of climate change can include damage from tidal storm surges and wide- spread flooding that inundate coastal highways (see example in Figure 3-11) and move floodwaters farther inland; fast-moving wildfires that damage and close highways for extended periods; and flash floods and mudslides 19 An examination of the range of potential impacts to Interstate infrastructure can be found in Special Report 290: Potential Impacts of Climate Change on U.S. Transportation (TRB and NRC 2008). In particular, see Chapter 3, âImpacts of Climate Change on Transportation.â
76 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM FIGURE 3-10 Increasing trend in number of severe-loss events in the United States due to natural catastrophes per year, by type of event, 1980â2016. NOTE: âCost with 95% CIâ denotes 95 percent confidence interval estimates of cost uncertainty; â5-year meanâ denotes the 5-year cost mean. SOURCE: Wuebbles and Jacobs (see Appendix G). TABLE 3-3 Interstate Highways Subjected to Closure because of Extreme Weather Events Interstate Highway Location Weather Event Year I-10 New Orleans, Louisiana Hurricanes Katrina and Rita 2005 I-110 Biloxi, Mississippi Hurricanes Katrina and Rita 2005 I-24 Nashville, Tennessee Flash flooding 2010 I-95 Connecticut, New Jersey, New York Superstorm Sandy 2012 I-10 Desert Center, California Flash flooding 2015 I-95 Fayetteville, North Carolina Hurricane Florence 2018 SOURCES: Breslin 2018; Miller 2012; TRB and NRC 2008; Williams 2015.
EMERGING CHALLENGES 77 that bury or wash out highways located in dry and drought-stricken re- gions. Moreover, when such damages occur, resultant disruptions to the operations of the Interstate Highway System can lead to even more serious outcomes by hindering emergency response and evacuation. As discussed in the next chapter, the impacts of climate change are expected to vary by region, and there is uncertainty about how they will evolve over time. It is certain, however, that transportation agencies across the country will need to revise how they plan, design, construct, operate, and maintain their highways to account for the impacts. It will be neces- sary to develop and implement robust design and construction standards that assume greater frequency and severity of extreme events, especially for core facilities, such as Interstates, major bridges, and emergency access and evacuation routes. Agencies will also need to assess and decide where and where not to build new assets. These efforts will require research, test- ing, and innovation in such areas as materials (e.g., asphalt and concrete mix designs), design criteria, construction techniques, and maintenance practices. They will also require translation of available climate projections into guidance and engineering standards that practitioners can use when planning and designing future infrastructure projects (Stahl et al. 2016). FIGURE 3-11 Section of I-45 submerged from the effects of Hurricane Harvey during widespread flooding in Houston, Texas (August 27, 2017). SOURCE: Reuters/Richard Carson.
78 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM While some assets with relatively shorter design lives, such as pave- ments, will provide early opportunities for upgrading Interstate highways to add resilience, the cost of redesigning and retrofitting certain Interstate infrastructureâsuch as elevating a bridge or highway or relocating a right- of-wayâwill be costly undertakings that will require a strategic, risk-based approach to investment decisions. The Interstate System includes many long-lived assets that nominally will not be replaced or undergo major reconstruction for years. Furthermore, past choices about where to locate some routes (e.g., in vulnerable coastal and riverine settings) cannot be undone without massive financial investments and community disruption. The challenge can be viewed broadly as a risk management âsystemsâ problem that will require states to identify the climate change impacts (e.g., sea level rise, extreme precipitation events) most relevant to their particular system, how those impacts are likely to manifest themselves (e.g., inunda- tion from storm surge), and which system segments are most vulnerable and present the greatest risk if action is not taken or is delayed. The choices are likely to require that future professionals be trained in adaptive design and risk management.20 Strategies for incorporating future changes in the natural environment into infrastructure planning and design are now emerging, prompted in part by recent disasters. Examples are FHWAâs 2014 release of Hydraulic Engi- neering Circular (HEC) 25, Highways in the Coastal Environment: Assess- ing Extreme Events, Volume 2 (FHWA 2014c) and 2016 release of HEC 17, Highways in the River Environment: Floodplains, Extreme Events, Risk, and Resilience, 2nd Edition (FHWA 2016d). These documents provide technical guidance and methodologies for incorporating climate change considerations, including sea level rise, storm surge and wave action, and extreme flood events, into the planning and design of highway projects in coastal and riverine environments. More tools of this type, along with quantitative measures and indicators of vulnerability and societal impacts, will be needed to inform resource allocation decisions by transportation agencies and to provide guidance for system planning, design, and opera- tions and maintenance activities. In this regard, states and FHWA can draw on experience garnered from such areas as seismic protection. Over the past 40 years, transportation agencies have been proactive in evaluating lessons learned from significant 20 It is notable that the American Society of Civil Engineersâ (ASCEâs) Committee on Adapta- tion to a Changing Climate is developing a manual of practice on adaptive design and adap- tive risk management. Adaptive design and risk management employ a methodology based on quantitative and probabilistic analysis of potential losses that support economic valuation and benefit-cost analysis of adaptive solutions based on real options. These adaptive solutions introduce the concept of exercising options to meet changes in the projected hazards in the future (NASEM 2018).
EMERGING CHALLENGES 79 earthquakes, researching solutions, and implementing improved design and retrofit guidelines and standards for bridges and infrastructure. California, for instance, has long used a risk-based approach for analyzing earthquake vulnerabilities to determine priorities for highway bridge retrofitting and replacement. These efforts have enabled the state to make effective overall use of investments for earthquake protection, but the total investment has nevertheless been substantial. The resources that will be needed to make the Interstate System more resilient to climate change promise to be large, but the exact level of that investment is unclear at this point, and may remain so for some time. SUMMARY This chapter has described pressing and emerging challenges that lie ahead if expectations for the Interstate Highway System are to be met. Commencing the enormous task of rebuilding the systemâs pavements before they become unserviceable over large segments of the system, while maintaining the systemâs aging bridges. Many of the Interstate pavements constructed in the 1950s and 1960s were designed for 20-year service lives but have now been in use more than 50 years without reconstruction of their base course and foundations, this despite much higher traffic loadings than projected. Even if one assumes that a pavement structure can last 50 years before requiring full reconstruction, the systemâs oldest segments are already long overdue for this work. Even most of the newest Interstate seg- ments, built in the 1980s and 1990s, will need to be rebuilt over the next 20 years. As this work is being accomplished on roadways, states will continue to need substantial resources to also invest in replacing and maintaining the integrity of their aging Interstate bridges. Meeting the growing demand for investments in physical capacity and active management of the urban system as metropolitan areas continue to experience most of the countryâs population and economic growth over the next few decades. Large portions of the Interstate System, especially in metropolitan areas, are already severely congested and unable to accom- modate the demands of local, interregional, and longer-distance travelers. Alleviating the problem of urban freeway congestion through such physical means as lane additions is expensive and sometimes impracticable, particu- larly when system right-of-way is constrained by land availability. Even if land can be acquired or existing right-of-way can be used more intensively, urban areas are expensive construction environments, and proposals for capacity expansion are often met with concern or outright opposition be- cause of community impacts. Ensuring that the system remains adaptable to continued evolution of the countryâs population and economy. Although thousands of miles of
80 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM high-quality highways other than Interstates connect the countryâs popula- tion centers, lack of access to the Interstate System may be viewed by some smaller communities and emerging cities as detrimental to their growth and development, particularly given that the system includes the countryâs main trucking corridors. The Interstate System was planned in the 1950s and considered complete in the 1990s despite a changing pattern of demand that is increasingly urban, western, and southern. Improving the systemâs safety performance as traffic volumes increase and the system is modified to increase capacity and throughput. Although the Interstates are the nationâs safest highways, they account for more than 5,000 traffic deaths annually. It will be necessary to continue to adopt state- of-the-art safety practices for the Interstates of the future to mitigate the additional risks arising from growth in traffic volume. Ensuring that the system is robust and adaptable to changing vehicle technologies, which entails avoiding premature investments and the intro- duction of standards that hinder or foreclose development pathways. Many new technologies have the potential to alter the operations and safety per- formance of the nationâs highway system, including the Interstates. Some of these technologies, such as driving-assist features and automated vehicles, are vehicle-centered, while others, such as real-time traffic analysis systems that inform traffic control devices, have a strong infrastructure orientation. Other technologies will involve connectivity of vehicles and infrastructure. Many of these technologies will have potential vulnerabilities that will re- quire protection from exploitation by outsiders. Developing strategies that address future climate conditions and incor- porating them into infrastructure planning and design, starting with the development of robust standards that assume greater frequency and severity of extreme weather events. When much of the Interstate System was being planned, designed, and built during the 1960s and 1970s, there was limited knowledge of the threat of greenhouse gases and how a changing climate could adversely affect the transportation system. Consequences include ris- ing sea levels and extreme weather-related events. Transportation agencies across the country will need to revise how they plan, design, construct, operate, and maintain their highways to account for these impacts. REFERENCES Abbreviations AAA American Automobile Association ATRI American Transportation Research Institute Auto-ISAC Automotive Information Sharing and Analysis Center BTS Bureau of Transportation Statistics
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