January 18, 2019

Transportation infrastructure is at risk from severe weather events compounded by climate change, according to the Transportation chapter of the Fourth National Climate Assessment (NCA4) report. Key findings from the chapter were the subject of a session on the National Climate Assessment at this week’s TRB Annual Meeting.

The report to Congress and the President, which is mandated every four years by the Global Change Research Act of 1990, analyzes the effects of human-induced and naturally-driven climate change on a variety of sectors, assesses societal consequences, and projects trends for the next 25 to 100 years.

The Transportation chapter of the NCA4 provides insight on the climate challenges specific to US transportation systems and the efforts to understand risks to transportation across all modes and geographies. The chapter’s report authors included federal and city government officials, academic researchers, and consulting and engineering practitioners.

TRB panelists included:

• Michael Culp, Team Leader of Sustainable Transportation and Resilience at the Federal Highway Administration
• Susanne DesRoches, Deputy Director of Infrastructure and Energy at the NYC Mayor’s Office of Recovery and Resiliency and the Office of Sustainability
• Anne Choate, Senior Vice President and Division Leader at ICF
• Rawlings Miller, Principal at WSP

Building on the overall themes of the current and previous NCA reports – namely, that the Earth’s climate is changing faster than at any other time in human history, there are widespread economic consequences to these changes, and human-driven change is expected to intensify in the future – the panelists provided insight on the following three “key messages” from the transportation chapter.

Transportation is at risk

A safe and reliable transportation system is at risk from extreme weather events like increases in heavy precipitation, coastal flooding, heat, wildfires, and changes to the average temperature. These risks result in different challenges to different geographic regions. For example, some of the 60,000 miles of roads and bridges in coastal regions are beginning to show signs of permanent inundation and increased flooding due to sea level rise, resulting in infrastructure damage and roadway congestion.

Despite regional differences, one extreme weather event can affect multiple modes of the transportation system simultaneously. For example, panelists spoke of rising temperatures causing bridges to expand and eventually crack, delays in air traffic as planes struggle to get the necessary lift in hotter temperatures, and weakening and bending rail tracks.

Consequences will be felt in both urban and rural areas

Regional differences can also be evaluated in terms of differential effects on urban and rural infrastructure. The panel discussed interdependencies inherent to urban energy, water, land, and transportation infrastructure. An extreme weather event affecting a city’s energy supply may also have a cascading influence on transportation, as was seen with a December 2017 power outage at Atlanta’s Hartsfield-Jackson International Airport.

However, urban areas tend to also have greater redundancy in transportation networks, with certain modes able to replace others during outages. For example, bus systems can operate additional service when subway tunnels flood. Rural areas, on the other hand, often lack this system redundancy. Pointing to major flood events in Colorado, Iowa, and Florida, the report demonstrates the social and economic dependence on single arterials in many rural American communities.

These urban and rural infrastructure vulnerabilities point to the need for infrastructure to be resilient to shocks and stresses so that people and goods can move seamlessly, a topic that Eno explored in a Fall 2018 webinar featuring speakers from 100 Resilient Cities. While resilience and asset management planning is increasingly required at the state and municipal levels, panelists spoke of the critical importance for using federal funding wisely when considering how to invest in infrastructure for the long term.

Vulnerability assessments can increase understanding of climate risks to transportation assets and services

According to the panelists, practitioners at transportation agencies across the country have indicated that they are experiencing unprecedented weather events and new challenges. Vulnerability assessments, which measure the direct and indirect implications of extreme weather events, showcase available funding opportunities and technical assistance, and provide improved climate modeling, are tools that are increasingly used by engineers, planners, and researchers to measure climate challenges.

Specifically, vulnerability assessments help practitioners to create links between the challenges they are experiencing and the strategies employed by others to mitigate or adapt to similar challenges. The NCA4 reviews and catalogs dozens of vulnerability assessments conducted between 2012 and 2016 to facilitate interstate and interregion learning.