Critical Interstate Improvements Identified in New Study

A new transportation study examining the needs of the U.S. Interstate Highway System has been released by the National Academies of Sciences, Engineering and Medicine.

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The study, a joint venture of WSP USA and Cambridge Systematics, conducted case study analysis and modeling to explore the impact of changing travel and technology trends, and their implications for the future of the Interstate Highway system.

WSP’s Jagannath Mallela served as a consultant for the Committee for a Study of the Future Interstate Highway System, working with Susan Binder and Richard Margiotta of Cambridge Systematics to conduct the case studies and modeling, as well as collecting information for the study with the committee’s guidance.

The final report, Renewing the National Commitment to the Interstate Highway System: A Foundation for the Future, was prepared as a component to support the objectives outlined in the Fixing America's Surface Transportation Act of 2015 (FAST Act).

The FAST Act called for the National Academies’ Transportation Research Board (TRB) to conduct “a study on the actions needed to upgrade and restore the Dwight D. Eisenhower National System of Interstate and Defense Highways to its role as a premier system that meets the growing and shifting demands of the 21st century.”

Although the interstate highway system comprises only 1.2 percent of the total U.S. public road system, it handles nearly 25 percent of the total vehicle miles traveled annually and almost 40 percent of the nation's total truck traffic.

“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,” according to the study. “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.”

With a network that has changed little since its inception, the aging Interstate Highway System alone serves more traffic than the entire U.S. road network served when the system was authorized in 1956.

Jagannath Mallela

Looming Challenges

The report explores pending and future federal investment and policy decisions concerning the federal interstate highway system. Congress asked the committee to make recommendations on the features, standards, capacity needs, application of technologies, and intergovernmental roles to upgrade the Interstate Highway System, and to advise on any changes in law and resources required to further the recommended actions. The report of the study committee suggests a path forward to meet the growing and shifting demands of the 21st century.

The comprehensive study covers multiple aspects of the Interstate Highway System, including bridges, highways, freight transportation, finances, safety, systems operation technologies, design, construction, environment, and looking ahead to the impact of data and information technology on transportation.

The committee identified major challenges confronting decision makers as they contemplate the future of the Interstate Highway System. Those looming challenges outlined in the study include:

  • 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.

Along with 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.


The Interstate Highway System serves more traffic than the entire U.S. road network served when the system was authorized in 1956.

Blueprint for Action

The models from the study calculated that if travel on the system grows at a modest pace comparable to the forecast U.S. population, transportation agencies will need to invest an average of $15 billion per year for improvements. These investments would need to be considerably larger if travel on the system grows at a pace closer to recent historical averages.

“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,” according to the report. “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.”

The study also outlined a “blueprint for action” that makes 10 recommendations based upon the extensive research findings. Some of those suggestions include:

  • Create an Interstate Highway System Renewal and Modernization Program (RAMP) by Congress that is focused on reconstruction deteriorated pavements, bridge infrastructure, adding traffic capacity and improving resiliency.
  • Address current and emerging demands to extend the Interstate System’s length and scope of coverage, and to remediate economic, social and environmental disruption caused by highway segments overly intrusive to communities and not vital to network and intermodal traffic.
  • Join with states to assess the foundational integrity of the system’s pavements and bridges, and identify where full reconstruction is needed.
  • To pay for RAMP, increase the federal motor fuel tax to a level commensurate with the federal share of the required investment, and adjust the tax as needed to account for inflation and changes in vehicle fuel economy.
  • Lift the ban on tolling of existing general purpose interstate highways.
  • Start planning the transition to more automated and connected vehicle operations.

“Today, the nation is experiencing, and can anticipate, new expectations for the system’s condition, performance and use,” the report stated. “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.”

The TRB study was conducted by a committee with balanced expertise in transportation issues, drawing from information provided by the highway industry, including highway owners, operators and users of the system, associations, private-sector stakeholders, and academia, among others. Research began in December 2016, and the completed 649-page book was released in late 2018.

Visit the TRB website to order or download the book.

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WSP USA was part of a joint venture to research the needs of the Interstate Highway System for a study.