Our nation's roads, bridges, rails, and port facilities—the foundation of the U.S. transportation system—are increasingly vulnerable to extreme events and sea level rise.

    Key points:

  • Increases in heavy precipitation, hot days, and coastal flooding are affecting the reliability and capacity of the U.S. transportation system.
  • The risk of major impacts to roads, bridges, port facilities, and railways near our coasts is increasing with sea level rise. More than 60,000 miles of coastal roads are already vulnerable to damage from extreme storms and hurricanes. Projections show that additional bridges, tunnels, and airports will become vulnerable as sea level rises.
  • Extreme weather events and high-tide flooding block traffic and require rerouting of regional freight patterns. Drivers already log 100 million vehicle-hours of delay due to high-tide flooding every year. Without changes, this number is projected to increase substantially.
  • Supply chains transport raw materials to manufacturing facilities and distribute products to consumers. Societal and economic consequences of extreme weather impacts can interrupt the transportation system and disrupt the flow of supply chains. These changes can have a disproportionate affect on vulnerable populations, especially in urban settings.
  • Challenges to the global transportation system—the complexity of intersecting networks, aging infrastructure, and dependencies on the energy and communications sectors—can be compounded by the impacts of climate change.

The U.S. transportation system is a series of interacting systems

Map showing annual freight tonnage by transportation mode

This map indicates the amount of freight moved across portions of the United States via different modes of transportation in 2007.

The U.S. economy depends on transportation infrastructure to get people where they want to go and to enable companies to gather materials and distribute goods. Climate-related disruptions of these systems can impede the continual flow of people and goods, leading to delays and product shortages, which can impact public health and local economies.

Photo of cars on a six-lane highway with entrance and exit ramps

The U.S. Interstate Highway System has almost 50,000 miles of controlled-access highways spanning the country.

The nation's transportation system is huge and complex:

  • The road system has approximately four million miles of mostly publicly owned roads and more than 600,000 bridges; these serve more than 230 million automobiles and light trucks, 10 million heavy trucks, and more than 70,000 transit buses.1
  • The rail system has 140,000 miles of mostly privately owned rail track, with most freight rail service provided by seven privately owned rail companies. Passenger rail service is provided by the federally owned Amtrak and a range of state and local rail service agencies.
Photo of subway train and customers on a station platform

The New York City Subway is one of the world's largest and busiest rapid transit systems.

  • Public transit agencies maintain some 12,000 miles of rails, supporting about 20,000 rail vehicles.2
  • A widespread network of privately owned pipelines move fuels and fuel products across the country, including 300,000 miles of pipeline for natural gas, 50,000 miles for crude oil, and 75,000 miles for petroleum products.
  • Coastal and inland waterways, largely used for freight, depend on a system of mostly federally operated locks and canals. Ports with diverse ownership service a mostly private fleet of 31,500 barges, 200 ocean-going U.S. flagships, and 9,000 other vessels.3
  • Air transportation is facilitated by the National Airspace System, which is operated by the federal government. The system includes a network of routes, radar systems, and air traffic control centers used by 7,500 mostly private, U.S.-registered commercial airliners, foreign airliners, and more than 200,000 general aviation aircraft.

Supply Chains move materials to manufacturers and consumers

Supply chains represent a shipper’s view of the transportation network. Each chain includes all the steps involved in transporting raw materials to processing and manufacturing facilities, and the steps to get finished products distributed to retailers and customers. As global trade among countries continues, supply chains of materials such as coffee from Africa or coconut oil from the Philippines span the whole world. As materials move from their source to their end users, interruptions in any portion of the chain can delay deliveries and increase costs. Some supply chains are only important to the makers and users of particular products. Other chains, for instance those that supply fuel, food, and other critical materials, are of importance to the economy.

Photo of downtown intersection inundated with seawater

Extreme high tides that occur a few times per year in low-lying coastal areas inundate roads and other infrastructure with seawater.

Assessing vulnerability to extreme events

Climate scientists project that current trends will result in higher temperatures, more severe precipitation events, longer and/or more frequent droughts, higher sea levels, and an increased frequency of strong hurricanes. Weather and climate impacts to the transportation system related to these changes include closures or disruptions in service, conditions that are unsafe for travel, damage to roads, bridges, and other infrastructure, and increased costs for maintenance, operations, and upgrades for transportation infrastructure. And interdependencies among transportation and other critical infrastructure sectors (such as energy) introduce the risk of significant cascading impacts on the operational capacity of urban transportation networks.

Engineers, planners, and researchers in the transportation field are increasing evaluating asset-specific and system-wide vulnerabilities in the transportation sector. These careful assessments will help them make informed decisions about the adaptive measures they could implement to address potential hazards. However, proactive implementation of resilience measures is still limited across the country. Resilient solutions for transportation facilities vary greatly depending on the climate stressor, the specifics of a given site, and the availability of funding for implementation

Individuals, businesses, and municipalities can increase their resilience to transportation delays and supply-chain issues through advance preparation. Building in redundancy—having more than one way to get to destinations—can keep traffic flowing. Changing conditions also call for new considerations in long-term planning for infrastructure and when selecting sites and building materials. Increasing redundancy of transportation components, and focusing on recovery planning can increase resilience.

This section is excerpted and abridged from the report Climate Change Impacts in the United States: The Third National Climate Assessment, (Chapter 5: Transportation) and Impacts, Risks, and Adaptation the United States: Fourth National Climate Assessment, Volume II: The Fourth National Climate Assessment, (Chapter 12, Transportation).

To learn more about the impacts of climate change and variability on transportation and supply chains, visit the subtopic pages:

Banner Image Credit

By Tim Evanson, CC BY-SA 2.0,, via Wikimedia Commons

Last modified
13 September 2020 - 11:46am