Adapting our transportation infrastructure to the effects of global climate change (GCC) is emerging as a new concern to consider as we rebuild our current system and as we plan and design future projects. The magnitude of the impact of GCC is difficult to predict with certainty, but there is a scientific consensus that impacts are occurring now and will continue to occur during the course of the century. These impacts have potential implications for where we locate and how we build our transportation infrastructure. However, tools and methodologies for evaluating and adapting to impacts are still in the early stages of development.
This paper includes background information and a summary of the key issues regarding adapting transportation infrastructure to climate change. The information in this paper is intended to be a starting point for discussions on the best ways to assess and respond to the risk of climate change impacts in developing and designing transportation projects.
The most likely effects of climate change include sea level rise due to melting land-based ice and from the expansion of water as a result of warmer temperatures; more extreme weather, including more severe precipitation events, more icing events, more frequent freeze/thaw cycles and heat waves; more intense hurricanes with potentially higher storm surges; and decrease in water supply in some areas of the country.
GCC effects on transportation infrastructure may vary based on the context in which they occur. For example, sea-level rise, coastal erosion, severity of tropical storms/hurricanes, storm surges, and subsidence, are all major concerns in coastal areas. Potential impacts on coastal infrastructure include: increased risk of bridge failure during storms, periodic or permanent inundation of coastal roads, more frequent repair of infrastructure after events, potential for increased bridge scour, and emergency evacuation concerns. Some effects may be more broadly experienced, across several contexts, such as temperature extremes and more severe precipitation events. Potential impacts might include increased pavement deterioration due to extreme temperatures, or an inability to implement or maintain mitigation commitments (such as storm water management facilities).
Adaptation is defined by the Pew Center on Global Climate Change as:
Actions by individuals or systems to avoid, withstand, or take advantage of current and projected climate changes and impacts. Adaptation decreases a system's vulnerability, or increases its resilience to impacts.
In areas where GCC effects are determined to be a significant issue for existing or proposed transportation infrastructure, adaptation considerations should be integrated throughout the transportation decision making process. How adaptation is addressed will vary depending on the level of transportation decision making, from transportation planning to maintenance and operations. The focus of this paper is on the implications for preliminary engineering and the NEPA process, and final design and implementation, so more detail is included for those sections below.
Implications for the transportation planning process
While there are no specific requirements in the planning regulations to directly address climate change, recent revisions to legislation have further incorporated energy and environmental considerations, which offer greater opportunities for state DOTs and MPOs to integrate adaptation considerations into the planning process. At the statewide or metropolitan planning level, decision makers consider broad, systematic effects of GCC on infrastructure to determine appropriate locations for future investments, inventory potentially affected transportation and environmental infrastructure, and identify the most vulnerable and critical infrastructure and mitigation assets. These inventories would support and inform planning and project funding and prioritization decisions. Traditional planning boundaries may need to be reconsidered to take into account different analysis scales when looking at GCC effects (for example watershed and floodplain areas as opposed to political boundaries). The transportation planning process also encompasses and considers emergency management.
Implications for preliminary engineering and NEPA
During project development, preliminary engineering and the NEPA process, a more detailed assessment of the environmental context is performed. This context, and assumptions regarding potential changes to the environment due to GCC effects, is essential in determining preliminary design parameters, screening out unreasonable alternatives, and addressing constructability and maintenance concerns. Life-cycle costs and benefit/cost methodologies may need to be adjusted to reflect long term cost implications of GCC effects on proposed alternatives. The way risk and uncertainty is evaluated in project development may also need to be reassessed due to potential GCC effects.
The use of the scoping process (early coordination with Federal, state and/or local agencies and the public) to ensure the engagement of GCC issues early in the project development process is essential to the success of the project. For example, for a bridge project in a coastal environment, a multi-disciplinary team consisting of GCC and coastal experts, along with hydraulics and bridge design specialists should be engaged during scoping to assist in the process. Another key issue that should be dealt with in scoping is the choice of methodologies and tools that will be applied to forecast future conditions. An example might include how to forecast shoreline locations for projects in coastal areas. Dealing with these issues early in the NEPA process helps prevent lengthy delays due to controversy and the need to conduct additional analysis and coordination.
At the preliminary design and NEPA stage, decision makers should begin to consider adaptive approaches to project design and implementation. For example, considering the significant uncertainty regarding GCC induced increases in tropical storm severity and sea level rise, flexibility can be incorporated into project alternatives to allow decisions made later in the design and implementation process to adapt to changing conditions. Monitoring of coastal conditions and the environmental context for a project can assist in keeping track of changes, and enable modifications in design and implementation to take place that will address these changes.
Implications for project design and construction
During final design, permitting, and construction of a project, design engineers determine/refine the parameters for project design and determine design and environmental standards to be applied to the project. Both design parameters and standards are potentially impacted when GCC effects and adaptation are considered. Regarding the design parameters for the project, many of the considerations here are similar to those discussed above with respect to the project context and methods to be applied to forecast conditions, although a more detailed analysis or study may be warranted. On the subject of design standards, modifications to existing standards may be needed due to the risk and uncertainty related to GCC effects. For example, designers may need to apply adaptation considerations to account for increased potential storm surge elevations and frequency and associated wave actions. These GCC effects change water level and additional forces applied to engineering structures, leading to designs that exceed existing design standards. This may raise concerns relative to escalating project costs and value engineering. Adaptation may also affect the specification of materials to be used for constructing the project. For example, designers may specify materials that are better suited to withstand additional loading because of the increased severity of storm events based on GCC. Adaptive management and monitoring approaches discussed above can be considered and/or refined during the final design process. A screening or review of projects in the design process may help determine if adaptive approaches should be incorporated.
Implications for operations and maintenance
Adaptation to GCC effects will also have implications for operations and maintenance. For example, inspection schedules may be accelerated to ensure that infrastructure remains structurally sound (such as the need for increased scour inspections after flood/storm events), or culverts may need to be maintained on a more frequent interval to deal with flash flood stream conditions. In addition, higher temperatures, periodic inundation due to storm surge, flooded drainage facilities, etc., may cause pavements to deteriorate more quickly, leading to increased maintenance activities and costs. GCC effects will likely have impacts on emergency management plans as well. For example, contingencies would likely need to be considered for at-risk infrastructure and their role in emergency evacuation operations. Emergency operations (e.g., evacuations) will be affected, as more frequent events will tax resources and more extreme events will lead to a loss in evacuation routes.
Anticipated changes in winter weather will also affect operations and maintenance. More frequent icing events will lead to increased maintenance activities and cost, as well as increases in crashes and traffic flow. More frequent freeze/thaw cycles will accelerate pavement deterioration and affect traffic flow and increase maintenance activities and cost. More extreme weather events will affect traffic flow, leading to reductions in capacity and mobility, as well as an increase in traffic incidents.
Climate change will also affect Emergency Relief (ER) programs. In the short term, it is likely that ER programs will need additional resources resulting from an increase in ER projects. These increases will likely be the result of increases in damage to transportation infrastructure due to more severe or more frequent storm events. However, if GCC effects are more comprehensively addressed in planning, project development, design, implementation, and maintenance and operations processes, the impact on ER programs should diminish due to planning, design and maintenance activities that adequately consider GCC-related risk.
The Potential Impacts of Climate Change on U.S. Transportation, Transportation Research Board Special Report 290 (2008).
Design Standards for U.S. Transportation Infrastructure: The Implications of Climate Change, Michael D. Meyer, Georgia Institute of Technology (2008).
Integrating Climate Change into the Transportation Planning Process, Federal Highway Administration (2008).
Impacts of Climate Change and Variability on Transportation Systems and Infrastructure: Gulf Coast Study, Phase I, US Department of Transportation Center for Climate Change and Environmental Forecasting (2008)
Adaptation Fact Sheet, Pew Center on Global Climate Change
Potential Impacts of Sea Level Rise on Transportation Infrastructure. US Department of Transportation Center for Climate Change and Environmental Forecasting (2008)