COMMITTEE FOR A STUDY OF THE FUTURE INTERSTATE HIGHWAY SYSTEM
TRANSPORTATION RESEARCH BOARD (TRB)
Summary
The Interstate Highway System has conferred both broad and deep benefits on the nation. Not only does it connect and integrate the transcontinental United States, but it also has been pivotal for more than 50 years in shaping and supporting the country’s demographic, spatial, economic, and social development. It functions as the main corridors for passenger and freight movement both within large urban agglomerations and between metropolitan and rural areas. It provides critical connections and services complementary to all of the country’s other passenger and freight transportation networks and their nodes, including railroads, marine ports, airports, public transit, and local road systems. Because its impacts reverberate across the transportation sector, society, and the economy, it is imperative that the Interstate System not only be preserved and rehabilitated, but also renewed and modernized to adapt to the country’s changing demographic, economic, climate, and technological landscape.
The Interstate Highway System’s future is threatened by a persistent and growing backlog of physical and operational deficiencies and by a number of large and looming challenges. Most of its segments are decades old, subject to much heavier traffic than anticipated, and operating well beyond their design life without having undergone major upgrades or reconstruction. These aging and heavily used segments, whose ranks will grow over the next 20 years, are poorly positioned to accommodate even modest projections of future traffic growth, much less the magnitude of growth experienced since the system’s inception in 1956.
As the nation moves further into the 21st century and as transformations in the vehicle fleet and vulnerabilities due to climate change place new demands on the country’s transportation infrastructure, the prospect of an aging and worn Interstate Highway System that operates unreliably is concerning. Unless a commitment is made soon to remedying the system’s deficiencies and to preparing it for the challenges that lie ahead, there is a very real risk that the system will become increasingly congested; far more costly to operate, maintain, and repair; less safe; incompatible with evolving technology; and vulnerable to the effects of a changing climate and extreme weather. The consequences from these deficiencies will spill over into all the passenger and freight modes that complement and connect to the system.
Congress called for the present study to inform pending and future federal investment and policy decisions concerning the Interstate Highway System. Specifically, Congress asked for recommendations on the actions necessary to restore and upgrade the system to meet the growing and shifting demands of the 21st century, through the next 50 years. The study’s findings, summarized below, point to the need for a major reinvestment in the system. Collectively, they serve as a call for action—carried out not through a series of incremental steps to repair the current system but through a concerted and adequately funded national campaign of system renewal and modernization patterned after the visionary program that initially produced the Interstates.
Looming Challenges
The committee identified major challenges confronting decision makers as they contemplate the future of the Interstate Highway System. These challenges include
- Commencing the enormous task of rebuilding the system’s pavements, bridges, and other assets and their foundations before they become unserviceable and less safe;
- Meeting the growing demand for investments in physical capacity, especially on the urban portions of the system, and for more active and innovative management of this capacity in large metropolitan areas that continue to experience most of the country’s population and economic growth;
- Ensuring that the system remains responsive to, and aligned with, continued changes in the geography and composition of the country’s population and economy, and that its connections with the other modes of local, interregional, and long-distance transportation are maintained and strengthened;
- Continually improving system safety as traffic volumes increase, new highway and vehicle technologies are introduced, and the system is modified to increase capacity and throughput;
- Ensuring that the system is robust and adaptable to changing vehicle technologies, and avoiding premature investments in assets and the introduction of standards that would hinder or even foreclose useful development pathways;
- Adopting funding mechanisms that are equitable and efficient, do not unduly impose the burden of payment on future generations or on less financially equipped groups, and do not disadvantage or divert resources from other highways and modes of passenger and freight transportation; and
- Developing and implementing strategies for incorporating future climate conditions into infrastructure and operations planning, starting with the development of design and construction standards that assume greater frequency and severity of extreme weather events.
An Investment Imperative
Because of the uncertainties associated with forecasting developments far into the future, specific uncertainties about the pace and form of motor vehicle automation, and the absence of appropriate modeling tools and data, the committee restricted its time horizon to the next 20 years for estimating system investment needs. During this period, the transition to vehicle automation is expected to remain at an early stage and have limited effects on Interstate travel. Investment needs over the 20-year horizon are likely to be dominated by a necessity to rehabilitate and reconstruct large portions of the Interstate System, which can be more confidently predicted than needs arising from changes in system use.
Most of the Interstate Highway System has far exceeded its design life or will do so over the next 20 years. Only limited planning and budgetary preparations have been made to fix the deterioration that has already occurred and to prevent the physical and operational deficiencies that will ensue. Recent combined state and federal capital spending on the Interstates has been on the order of $20–25 billion annually (Figure S-1). The information gathering, modeling, and case studies that informed this study indicate that this level of spending is too low— by at least 50 percent—just to proceed with the long-deferred rebuilding of the system’s aging and deteriorating pavements and bridges. The committee estimates that investments averaging more than $30 billion per year will be needed over the next 20 years to repair and reconstruct these assets from damage already done and that is forthcoming from the effects of age and further use. Figure S-1 shows how these rehabilitation and reconstruction investment needs do not change much across different scenarios of growth in vehicle miles traveled.
Along with these substantial investments in pavement and bridge rehabilitation and reconstruction, additional investments will be required to expand and manage the Interstate Highway System’s capacity to handle future traffic. Investments that will be required to accommodate this traffic demand are much more difficult to project. Significant capacity additions will likely be required because of growth of urban areas that are not well connected to the Interstate System and because of the continued growth of large metropolitan regions. However, the size, location, and timing of these needed additions will depend on a host of factors related to changes in the population and economy, how travelers respond to congestion and the supply of new capacity, whether new capacity is restricted to specific users, and the availability of options other than Interstate travel. Transportation agencies, especially in urban areas, may substitute more active operations and demand management measures, such as congestion tolling, for spending on lane widening and other physical additions to Interstate highways, particularly where the acquisition of additional right of way is very expensive or unacceptable to local communities. Although connected and automated vehicles are likely to have limited effects on travel demand in the nearer term, expectations about their longer-term impact may influence transportation agency decisions about whether and where to invest in Interstate capacity, especially in 10 to 15 years.
In addition to the many uncertainties and interdependencies noted above, the committee found that the available data and models do not have the capability to predict the effects of changes in capacity on travel demand across broad portions of the Interstate network. By stretching the national-level modeling capabilities that do exist and using a range of historically informed rates of growth in future Interstate travel, the committee could, at best, make rough approximations of the magnitude of spending that might be needed for physical and operational capacity improvements over the next 20 years. The models calculate that if travel on the system is assumed to grow at a modest pace comparable to the forecast U.S. population (0.75 percent growth annually), transportation agencies will need to invest an average of $15 billion per year for such improvements. These investments would need to be considerably larger, by about 50 to 100 percent, if travel on the system is assumed to grow at a pace closer to recent historical averages (Figure S-1).
Thus, an approximation of the total state and federal spending that will be needed to renew and modernize the Interstates over the next 20 years averages $45–70 billion per year. The figures in this range are 2 to 3 times higher than current spending levels, and even 50 percent higher when only considering the outlays that will be required for the pavement and bridge upgrades that can be projected with higher confidence. However, even these estimated investment levels may be inadequate. Because of the lack of analytical tools and adequate databases, they do not include the funding required to reconfigure and reconstruct many of the Interstate System’s roughly 15,000 interchanges, nor do they include the resources needed to make the system more resilient to the effects of climate change, add special-purpose and managed lanes that can allocate system capacity more efficiently in and around metropolitan areas, and “rightsize” the system’s scope of coverage through network extensions and in some cases replacement and modification of controversial urban segments. While these investment needs could not be estimated even roughly for this study, they are certain to require billions, and perhaps tens of billions, in additional annual spending.
Recommendations
The original Interstate Highway Construction Program was underpinned by a long-term, collaborative commitment among the states and the federal government. A comparable partnership is needed to renew and modernize the system and to ensure that it is resilient and responsive to the changing demands of users. Central to that partnership is federal leadership and a resolve to restore the Interstate Highway System’s premier status and ensure that this status is no longer allowed to obsolesce. The recommendations that follow provide a blueprint for Congress to act on that resolve.
Congress should legislate an Interstate Highway System Renewal and Modernization Program (RAMP). This program, presumed to be pursued without sacrificing normal ongoing system maintenance and repair, should focus on reconstructing deteriorated pavements, including their foundations, and bridge infrastructure; adding physical capacity and operations and demand management capabilities (e.g., tolling) where needed; and increasing the system’s resilience. RAMP should be modeled after the original Interstate Highway System Construction Program by
Reinforcing the traditional program partnership in which the federal government provides leadership in establishing the national vision for the overall system, the bulk of the needed funding, and overall standards, while states prioritize and execute projects in their continued role as owners, builders, operators, and maintainers of the system;
- Ensuring that the federal share of project spending is comparable to the 90 percent share of the original Interstate Highway System Construction Program;
- Committing the federal government to supporting projects from start to finish, but with a cap on total federal funding (i.e., a cost-to-complete approach); and
- Developing transition plans for updating and incorporating standards for system uniformity and safety to accommodate changing vehicle and highway technologies, environmental and climate conditions, and usage patterns.
Congress should, as a near-term step, (1) increase the federal motor fuel tax to a level commensurate with the federal share of the required RAMP investment, and (2) adjust the tax as needed to account for inflation and changes in vehicle fuel economy.
To ensure that the federal government’s long-term commitment to RAMP is not threatened by declining fuel tax revenues as the vehicle fleet and its energy sources evolve, Congress should prepare for the need to employ new federal and state funding mechanisms, such as the imposition of tolls or per-mile charges on users of the Interstate Highway System.
To provide states and metropolitan areas with more options for raising revenue for their share of RAMP investments and for managing the traffic demand on and operations of Interstate segments that offer limited opportunity for physical expansion, Congress should lift the ban on tolling of existing general-purpose Interstate highways. As a condition for imposing those tolls, states should be required to assess their impact on current users and offer alternative mobility options for those users significantly and disproportionately harmed by the tolls.
A “rightsizing” component of RAMP should address current and emerging demands to extend the Interstate System’s length and scope of coverage, and to remediate economic, social, and environmental disruptions caused by highway segments that communities find overly intrusive and are not deemed vital to network and intermodal traffic. Congress should direct the U.S. Department of Transportation and the Federal Highway Administration to develop criteria for such system rightsizing using a consultative process that involves states, local jurisdictions, highway users, and the general public. The criteria and their development should take into account the interest in ensuring
- Adequate system connectivity to accommodate network flows of Interstate travel and commerce, including traffic from other important passenger and freight transportation modes;
- System access to growing centers of population and economic activity;
- System resilience through redundancy or other means as appropriate; and
- Responsiveness to national defense needs.
Concluding Comments
Implementation of the above recommendations, together with the recommended complementary actions summarized in Box S-1, would represent a fundamental shift away from a federal policy that has lost focus on the Interstate System and the commitment to funding it adequately. These actions would restore the system’s premier status within the nation’s highway program in a manner that is aggressive and ambitious, although by no means novel. Taking these actions would rekindle a tried-and-true federal–state partnership; reinforce the system’s long-standing reliance on user fees to provide a fair, adequate, and reliable source of funding; and reassert the forward-looking vision that was instrumental to the genesis of this crucial national asset more than a half-century ago. At that time, the nation’s leaders endorsed a modern highway system that would confer large and lasting societal and economic benefits, a vision whose realization required a strong and continuing national commitment. Today, the nation is experiencing, and can anticipate, new expectations for the system’s condition, performance, and use. Meeting those expectations will require the same forward-looking outlook and commitment that informed the system’s creation—a rededication to that original vision that reshapes and reequips the system to serve generations to come.
Download full version (PDF): Renewing the National Commitment to the Interstate Highway System
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The Transportation Research Board (TRB) provides innovative, research-based solutions to improve transportation. TRB is a program unit of the National Academy of Sciences, Engineering and Medicine, a non-profit organization that provides independent, objective, and interdisciplinary solutions.
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