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From page 49... ... 3 Emerging Challenges Having served as the backbone of the country's 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. Read the entire page →
From page 50... ... 50 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM and interregional coverage and connectivity, shifts in the geography of the country's 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 demand attention, new ones are emerging that may prove even more vexing. Read the entire page →
From page 51... ... EMERGING CHALLENGES 51 REBUILDING THE SYSTEM'S FOUNDATION At a Glance • As the foundation of a pavement continues to deteriorate, resurfacing will no longer rectify the damage, and the pavement structure will need to be rebuilt from the subbase up. • Most segments of the Interstate Highway System retain their original underlying structure. Read the entire page →
From page 52... ... 52 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM cases in which Interstate segments have already undergone full reconstruction, 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. Read the entire page →
From page 53... ... 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, 14–16) Read the entire page →
From page 54... ... 54 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM roughness or smoothness, suggest that states have been improving the condition 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 regain smoothness have confirmed that it produces diminishing returns over time -- that is, shorter periods of serviceability between successive overlays. Read the entire page →
From page 55... ... 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. Read the entire page →
From page 56... ... 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 service 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. Read the entire page →
From page 57... ... EMERGING CHALLENGES 57 with pavements, the long-term deferral of major repair work can have catastrophic effects on bridges. States have therefore been required to pay close attention to their Interstate bridges as they age and sustain damage from usage or natural phenomena. Read the entire page →
From page 58... ... 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) Read the entire page →
From page 59... ... EMERGING CHALLENGES 59 EXPANDING AND MANAGING URBAN SYSTEM CAPACITY At a Glance • 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 lanemiles on the system grew by only 25 percent. Read the entire page →
From page 60... ... 60 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM largest 75 regions -- each having more than 500,000 people -- account for about half the U.S. population (Frey 2016) Read the entire page →
From page 61... ... 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 noncongested periods (Schrank et al. Read the entire page →
From page 62... ... 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. Read the entire page →
From page 63... ... 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 generalpurpose lanes (TRB 2016) Read the entire page →
From page 64... ... 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 highoccupancy vehicle (HOV) Read the entire page →
From page 65... ... 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 projects -- I-66 outside the Beltway in Northern Virginia and the I-405 express toll lanes in Seattle -- are analyzed as case studies in this report (see Table 3-1 and Appendix I) Read the entire page →
From page 66... ... 66 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM a 550-mile network of toll-managed lanes (Interstate and non-Interstate) Read the entire page →
From page 67... ... 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] Read the entire page →
From page 68... ... 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* Read the entire page →
From page 69... ... EMERGING CHALLENGES 69 connected to the Interstate System (FHWA n.d.-c) Read the entire page →
From page 70... ... 70 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM freight corridors -- known as the Congressional High-Priority Corridors -- whose highways would be upgraded and designated as part of the Interstate System. The CANAMEX Trade Corridor was prescribed to create an Interstate route parallel to I-5 farther to the east (I-15 spanning from San Diego County, California, to Alberta, Canada) Read the entire page →
From page 71... ... EMERGING CHALLENGES 71 within a single state or across two or three states. These additions are intended to serve such purposes as connecting the core cities of expanding megaregions (e.g., Raleigh–Norfolk corridor) Read the entire page →
From page 72... ... 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) Read the entire page →
From page 73... ... 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. Read the entire page →
From page 74... ... 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 prominent 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. Read the entire page →
From page 75... ... EMERGING CHALLENGES 75 instance, environmental factors such as the expected duration and intensity of rainfall affected design choices about subsurfaces, materials, and drainage 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 assets more resilient to the consequences of climate change is now widely recognized, in part because of recent experience and in part because of forecasts by much of the science community. Read the entire page →
From page 76... ... 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, 1980–2016. NOTE: "Cost with 95% CI" denotes 95 percent confidence interval estimates of cost uncertainty; "5-year mean" denotes the 5-year cost mean. Read the entire page →
From page 77... ... EMERGING CHALLENGES 77 that bury or wash out highways located in dry and drought-stricken regions. 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. Read the entire page →
From page 78... ... 78 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM While some assets with relatively shorter design lives, such as pavements, will provide early opportunities for upgrading Interstate highways to add resilience, the cost of redesigning and retrofitting certain Interstate infrastructure -- such as elevating a bridge or highway or relocating a rightof-way -- will 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. Read the entire page →
From page 79... ... 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. Read the entire page →
From page 80... ... 80 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM high-quality highways other than Interstates connect the country's population 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 country's 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. Read the entire page →
From page 81... ... EMERGING CHALLENGES 81 DOT Department of Transportation Caltrans California DOT FHWA Federal Highway Administration NASEM National Academies of Sciences, Engineering, and Medicine NHTSA National Highway Traffic Safety Administration NIST National Institute of Standards and Technology NOAA National Oceanic and Atmospheric Administration NRC National Research Council NYCEDC New York City Economic Development Corporation TRB Transportation Research Board U.S. Read the entire page →
From page 83... ... EMERGING CHALLENGES 83 Mahoney, J Read the entire page →
From page 84... ... 84 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM TRB. unpublished. Read the entire page →

From page 49...

... 3 Emerging Challenges Having served as the backbone of the country's 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.