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Potential Impacts of Climate Change on U.S. Transportation 4 Challenges to Response This chapter explores the challenges and constraints faced by transportation professionals as they begin to confront projected impacts of climate change. The chapter begins with an overview of how the U.S. transportation system is organized and how investment and operating decisions are made. These organizational arrangements and planning approaches influence how transportation decision makers consider the issue of climate change and help explain why responding poses difficult challenges—the next topic of discussion. A framework for addressing the uncertainties and analyzing the trade-offs associated with adaptation to climate change is then introduced. The chapter ends with the committee’s findings, suggesting opportunities for meeting the challenges to response. DECISION MAKING IN THE TRANSPORTATION SECTOR Organization and Funding Responsibility for transportation infrastructure is decentralized and shared between the public and private sectors (see Table 4-1). Highways, bridges, and public transportation infrastructure are owned and operated by state and local governments.1 Major funding for capital improvements—and in the case of public transportation, rolling stock (e.g., transit buses, railcars)—is provided by the federal government, with matching 1 Highways and bridges on federal lands are an exception, as are privately owned toll roads. In addition, the vehicles that use the highway system are privately owned, except for transit buses (see Table 4-1).
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Potential Impacts of Climate Change on U.S. Transportation TABLE 4-1 Transportation System Responsibility System Owner–Operators Capital Improvements Land Transportation Highways and bridges Infrastructure State and local governmentsa Federal funding for major highways with required local match Vehicles Privately owned and operated NA Public transportation Infrastructure Local governments and independent authoritiesb Federal funding with required local match Rolling stock Publicly owned and operated NA Railroads Infrastructure Privately owned and operated Private funding Rolling stock Privately owned and operated NA Pipelines Privately owned and operated Private funding Marine Transportation Inland and coastal navigation channels, St. Lawrence Seaway, and associated navigation aid (all infrastructure) Federal government through the U.S. Army Corps of Engineers and U.S. Coast Guard Joint federal and nonfederal public funding, user fees Ports and terminals Infrastructure State and local governments, independent authorities, and private entities Public and private funding Vessels Privately owned and operated NA Air Transportation Infrastructure Local governments and independent authorities Federal funding, supplemented with state and local grants and passenger facility charges Vehicle fleet Privately owned and operated NA Note: NA = not applicable. aThe exceptions are highways on federal lands and private toll roads. States are responsible for highways and bridges on major roads. Cities are responsible for major arterial streets in some metropolitan areas. bSome public transportation services are contracted out to private providers.
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Potential Impacts of Climate Change on U.S. Transportation requirements from other governmental levels. Railroads and pipelines are privately owned and operated, although the federal government has regulatory oversight over railroad and pipeline safety.2 Ports are joint public–private operations. Typically, an independent authority or public entity owns the land and sometimes the landside facilities, which are then leased to private operators, generally on a long-term basis. Major improvements, such as dredging of harbors and channels, are federally funded through the U.S. Army Corps of Engineers, with required cost sharing.3 The St. Lawrence Seaway system is jointly operated by the U.S. government and Canada through management corporations established expressly for this purpose, while the inland waterway system, including upkeep of the lock system, is operated by the U.S. government through the U.S. Army Corps of Engineers, also with cost-sharing arrangements. Airports are publicly owned and operated by local governments or independent authorities. At the major hub airports, the airlines often operate their own hangars and maintenance facilities. Many airport capital improvements are federally funded, supplemented with state and local grants and passenger facility charges. In sum, decision making in the transportation sector is a shared responsibility among many governmental owner–operators and the private sector, largely decentralized, and modally focused. Infrastructure Service Lives Transportation infrastructure is designed to perform for a wide range of service lives (see Table 4-2).4 Roads are among the shortest-lived facilities, with surfaces that must be repaved every 10 to 20 years.5 Bridges, locks, and pipelines are among the longest-lived—designed for a 50- to 100-year service life—although many of their components (e.g., bridge decks) must be rehabilitated more frequently. Transportation facilities 2 The Federal Energy Regulatory Commission regulates the siting of new natural gas pipelines, and the U.S. Department of Transportation requires 3 feet of cover at initial construction of an oil pipeline. 3 There is some privately constructed and maintained infrastructure (e.g., channels to private terminals, private berthing areas). 4 Service life can be defined as the length of time a facility will remain in use to serve its intended function. This will often exceed the facility’s design life or the period of time used for economic analysis of project benefits and costs. 5 Typically, the road base is far more durable, unless it is compromised by poor drainage or other adverse conditions.
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Potential Impacts of Climate Change on U.S. Transportation TABLE 4-2 Transportation Infrastructure Design Lives Transportation Mode Expected Infrastructure Design Life (years) Highways, bridges, and tunnels Pavement 10–20 Bridges/culverts 50–100/30–45 Tunnels 50–100 Public transportation Rail track Up to 50 Rail Track Up to 50 Marine transportation Locks and dams 50 Docks and port terminals 40–50 Air transportation Runway pavements 10 Terminals 40–50 Pipeline 100 Note: Design lives are averages. Much of the infrastructure operates far beyond its design life. Source: Meyer 2006. with shorter design lives provide numerous opportunities for engineers to adapt to the impacts of climate change, such as by use of more heat-resistant paving materials to withstand the more extreme temperatures projected for some U.S. regions. Opportunities for adaptation—for example, elevating a bridge to accommodate expected sea level rise—are fewer for longer-lived facilities, which are rehabilitated or retrofitted at much longer intervals. In practice, many transportation facilities perform well beyond their design lives. Moreover, the most critical decision is where to locate a facility initially. Once the right-of-way and alignment for a facility have been established, such as for a highway or rail line, relocating the right-of-way, as might be required in coastal areas experiencing sea level rise, would be enormously expensive. Thus, investment choices made today about the location, retrofitting, and rehabilitation of transportation infrastructure will have far-reaching consequences for the ability of transportation infrastructure to accommodate climate change and for the costs of any necessary adaptation.
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Potential Impacts of Climate Change on U.S. Transportation Long-Range Planning and Investment Decisions For each mode, transportation professionals engage in planning for long-term capital improvements to infrastructure assets. Below is a brief summary of the planning process for publicly and privately owned infrastructure and the implications for addressing climate change. Publicly Owned Infrastructure Planning and investment decisions for publicly owned land transportation infrastructure are made within the framework and requirements defined by the planning provisions contained in legislation; codified in Title 23, U.S.C.; and most recently amended in August 2005 by the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, known as SAFETEA-LU. State departments of transportation and metropolitan planning organizations (MPOs), working in coordination with local governments, have lead responsibilities for planning.6 The transportation planning process has two principal products: a long-range transportation plan and a short-term transportation improvement program. Because the infrastructure is largely in place, the vast majority of capital improvement projects involve retrofitting or upgrading the existing transportation system or providing new capacity at the margin. Each state and metropolitan area with an MPO prepares a long-range plan, looking ahead 20 to 30 years. The plans incorporate forecasts of population, economic growth, and land use patterns to help determine the locus and extent of demand for passenger and freight travel and supporting transportation infrastructure needs. The second product—a transportation improvement program—provides a list of short-term capital improvement projects, reflecting available funding, which is updated on a 4-year cycle. Joint Public–Private and Privately Owned Infrastructure Ports generally have a short planning horizon—5 to 10 years—because of the highly competitive nature of port business operations. Analyses of major capital improvements, however, such as landside facilities—warehouses, 6 The Highway Act of 1973 required the establishment of MPOs in urbanized areas with a population of more than 50,000 and dedicated a small portion of each state’s funding from the Highway Trust Fund for this purpose. MPOs are composed primarily of local elected officials whose purpose is to facilitate decision making on regional transportation issues.
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Potential Impacts of Climate Change on U.S. Transportation terminals, berths, rail links, and truck access roads—many of which have 40- to 50-year design lives, require forecasting of costs and expected returns over a much longer planning period. Similarly, the planning horizon for capital improvements to long-lived locks and dams along inland waterways is about 50 years. Airports have 20- to 30-year capital improvement plans for landside investments. Because many of these improvements are federally financed, the Federal Aviation Administration, as well as local airport authorities and local planners, is involved in the development of long-range plans for airport infrastructure. The planning cycle for privately owned infrastructure—railroads and pipelines—is handled by individual companies through their capital budgeting process. Railroads are characterized by their capital intensity and large fixed investments. Even when a fully functional network is in place, large annual capital investments must be made to provide operating equipment (e.g., locomotives, freight cars, maintenance vehicles, computer and signaling equipment) and maintain the physical right-of-way.7 Capital budgets are part of strategic plans that look 5 years out and annual financial plans that identify the available budget for capital outlays each year. Analyses of individual capital projects forecast costs and returns over 20- to more than 30-year lifetimes for major facilities, such as a double-tracking project or a new marshaling yard.8 Pipelines involve a large initial investment; assets are designed to be very long-lived (about 100 years); and there are few new entrants. Pipeline companies conduct market forecasts looking ahead 5 years at most. Planning for capital improvements follows the normal private-sector capital budgeting process (i.e., project analysis using present value calculations over asset lifetimes, minimum expected rates of return for project selection, and annual capital budgets). In sum, public and private transportation infrastructure providers are making short- and long-term investment decisions every day that have implications for how well the transportation system will respond to climate change in both the near and long terms. 7 These investments tend to be uneven or “lumpy,” however, because equipment, such as railcars, is purchased in batches. 8 Note, however, that discounting of future benefits at typical discount rates means that for financial purposes, benefits beyond, say, 20 years will be of diminishing importance.
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Potential Impacts of Climate Change on U.S. Transportation Operational and Emergency Planning Transportation professionals in both the public and private sectors also engage in operational planning to respond to short-term congestion, delays, and disruptions to system operations. Transportation professionals are keenly aware of the effects of weather on system performance and already address the impacts of weather on operations for a diverse range of climate conditions. For example, many departments of transportation have well-organized snow and ice control operations that can consume up to 40 percent of annual highway operating budgets in some northern U.S. states. Others are organizing to achieve better management of traffic congestion and incident control by establishing transportation management centers.9 Climate changes are expected to affect transportation primarily through climate extremes, such as more severe tropical storms and flooding from intense rainfall. One of the probable outcomes is the growing importance of transportation to emergency response and evacuation. The organizational arrangements necessary to support this interaction are generally not well developed, although some regions have been more proactive in this regard. For example, Florida has a well-organized multigovernmental approach to emergency planning and evacuation for hurricanes that includes transportation. Hurricanes Katrina and Rita provided a wake-up call to many governments in the Gulf Coast region, which have since improved emergency plans and evacuation strategies. The events of September 11, 2001, were instrumental in focusing attention on the need for emergency plans and evacuation strategies and in underscoring the critical support transportation can provide. In practice, however, transportation is not always well integrated into these plans. Emergencies that involve multistate geographic areas and require a regional response are particularly difficult, as Hurricane Katrina illustrated (Deen 2006). In the longer term, critical infrastructure that serves as evacuation routes or egress points may itself be threatened by climate change. For example, highways in low-lying coastal areas could become endangered as encroaching sea level rise combines with storm surge to make these routes impassable. 9 For more detail, see the paper by Lockwood (2006) commissioned for this study. See also the discussion about transportation management centers in Chapter 5 (Box 5-1).
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Potential Impacts of Climate Change on U.S. Transportation CHALLENGES POSED BY CLIMATE CHANGE Climate change poses a complex set of challenges that in many ways are new and different for transportation planners and decision makers, and this may help explain why there is little consensus on the issue or how to address it.10 The lack of a consistent response may also stem from resource constraints and an absence of adequate information and guidance. Differences in Planning Horizons Climate scientists describe the future in terms of outcomes that unfold over decades to centuries. One of the reasons for these long time frames is that the inherent variability of the climate makes it difficult to separate the “signal from the noise” in making short-term (i.e., less than 25 years) projections. For many public-sector transportation planners, long-term planning horizons rarely exceed more than 30 years; 20 to 25 years is the norm. Port, rail, and pipeline providers have much shorter planning horizons—5 years at most for strategic plans—although many of their assets are designed to be much longer-lived, and capital project analyses reflect these longer time frames. Thus, many transportation planners perceive that impacts of climate change will be experienced well beyond the time frame of their longest-term plans, not realizing that climate changes are already occurring and that investment decisions made today will affect how well the infrastructure accommodates these and future changes. Treatment of Uncertainty The issue of climate change introduces uncertainties with which transportation planners are unfamiliar and uncomfortable. Climate scientists describe the future in probabilistic terms with a portfolio of plausible scenarios and outcomes that are constantly refined and revised as new knowledge accumulates. Uncertainties exist with regard to the rate of climate change and the extent of its impacts, even for those changes about which climate scientists have the greatest confidence, such as warming temperatures and sea level rise. These uncertainties make it difficult to 10 See the paper by Dewar and Wachs (2006) commissioned for this study for a more complete discussion of many points made in this section.
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Potential Impacts of Climate Change on U.S. Transportation plan and design infrastructure that can accommodate these impacts. The likelihood of climate extremes and surprises only exacerbates the problem. Moreover, knowledge about climate change impacts is likely to change over time, requiring a dynamic decision process that can adapt to new information and accommodate feedback. In contrast to climate scientists, transportation professionals tend to focus on “knowns.” Metropolitan transportation planners, for example, typically provide a single vision of the future on the basis of “best available” forecasts of population, employment, housing, and development that drive transportation infrastructure needs. Infrastructure is built to meet the forecast demand, often without fully incorporating uncertainties associated with the predictions. Unexpected, unplanned events, such as earthquakes, hurricanes, and floods, challenge the system, but a combination of traveler adaptability and system redundancy has enabled transportation infrastructure providers thus far to maintain operations with surprisingly little disruption. Perhaps for these reasons, regional transportation planners appear to be satisfied with their performance. A national survey of regional planning agencies, for example, revealed that the majority rated their performance as acceptable and their models as adequate or better. Only a few, however, had simulated the effects of removing key links from their systems or assuming large and irregular fluctuations in traffic flows in some corridors, such as might occur if tropical storms become more severe or intense precipitation and flooding become more frequent in some regions (Dewar and Wachs 2006). Poor Alignment Between Climate Change Impacts and Transportation Organizational Arrangements The decentralized and modally focused organizational structure of the transportation sector may not align well with climate change impacts, which do not always follow modal, jurisdictional, or corporate boundaries. Sea level rise and flooding from intense precipitation, for example, can affect individual transportation facilities, but they are also likely to have widespread impacts requiring the response of multiple infrastructure providers. Some climate changes, such as more frequent intense tropical storms (Category 4–5 hurricanes), will require regional or even multistate responses that transportation institutions are poorly configured to address.
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Potential Impacts of Climate Change on U.S. Transportation Regional planning organizations exist, but regional government does not. Multistate action is difficult, as Hurricane Katrina illustrated. Resource Constraints Climate change poses the possibility of significant, long-lasting impacts on transportation infrastructure and system performance that are likely to be widespread and costly in human and economic terms. Most other challenges confronted by the transportation sector, even extreme weather events such as Hurricane Katrina or earthquakes, cause significant damage, but the effects tend to be local and temporary. By contrast, climate changes in some U.S. regions may necessitate permanent changes. Over time, for example, roads, rail lines, and airport runways in low-lying coastal areas may become casualties of sea level rise, ultimately requiring relocation or expensive protective measures (e.g., levees, which themselves would be subject to catastrophic failure, as was experienced during Hurricane Katrina). Resistance to Change Transportation planners and engineers typically extrapolate from historical trends to forecast future trends and conditions that influence their investment choices and operating plans. However, the past will not be a reliable guide for future plans and designs as they relate to climate. Climate scientists caution that climate change will usher in a new regime of weather and climate extremes, likely falling outside the range for which many existing transportation facilities were designed. Faced with a new problem such as this predicted break in trend, transportation professionals typically adopt incremental rather than radical solutions. This tendency to favor proven methods and practices is understandable, particularly for engineers, who are designing infrastructure expected to provide reliable service for decades, and in view of the uncertainties about the rate of climate change and the magnitude of its effects. Nevertheless, reinforced by conservative institutions, regulatory requirements, and limited funding, this way of thinking can hamper timely responses to issues such as climate change that involve risk and uncertainty. Interviews with transportation planning officials conducted for the U.S. Department of Transportation’s (USDOT’s) Gulf Coast study by Cambridge Systematics, Inc. (2006) are illustrative of prevailing attitudes.
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Potential Impacts of Climate Change on U.S. Transportation The interviews were conducted in spring 2006, when the impacts of Hurricanes Katrina and Rita were very much on the minds of local planners. Understandably, local officials were concerned with the immediate problems of rebuilding and recovery from the hurricanes. When questioned about the possibility that climate change could bring about more storms of the intensity of Katrina or Rita in the future, however, many local officials expressed skepticism or pleaded ignorance. Others opted for a literal interpretation of SAFETEA-LU’s planning guidance, which does not require consideration of climate change, or pointed to federal policies that allow replacement of facilities only as they are currently designed, preventing consideration of design modifications that could provide for adaptation to potential climate change impacts (e.g., elevated bridges to accommodate sea level rise, storm surge, and wave action).11 Some officials interviewed believed that Federal Highway Administration regulations prevented them from considering any changes that would extend beyond the time horizon of their long-range plans.12 Still others identified limited current funding that, in combination with uncertainties about the rate and timing of projected climate changes, disinclines planners to give more attention to the issue. Lack of Relevant Information Even those transportation professionals who are aware of the importance of climate change and are already addressing its impacts, such as the planners and engineers in Alaska who are managing the effects of melting permafrost, indicate that they often lack sufficiently detailed information on which to take appropriate action. Climate scientists tend to describe projected climate changes in terms of global averages and confidence levels for global, continental, or large subcontinental regions because climate models have the greatest fidelity at these levels of analysis. In addition, studies of the impacts of climate change—with the exception of the handful of studies reviewed in the previous chapter—have not focused on 11 The Federal Highway Administration, however, has granted exceptions and is rethinking its regulations and guidance for design of bridges in a coastal environment (Meyer 2006). 12 Section 6001 of SAFETEA-LU references a 20-year forecast period for long-range transportation plans. Many states and MPOs, however, are using a 20- to 30-year time horizon.
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Potential Impacts of Climate Change on U.S. Transportation BOX 4-1 California Seismic Retrofit Program for Bridges Following the Loma Prieta earthquake in 1989, the California Department of Transportation (Caltrans) faced the enormous task of prioritizing its inventory of structures throughout the state for seismic retrofit. Approximately 25,000 bridges on state and local highways required evaluation. Because of this large number of bridges, a simple and computationally manageable prioritization methodology had to be devised. The goal was to identify and rank the most seismically vulnerable bridges in the state so the available resources could be used in the most efficient manner possible. The process began with establishing a required performance standard. For most bridges, the minimum standard was “no collapse” during a major seismic event to prevent loss of life. However, damage to the structure was acceptable provided that the structure itself remained intact and could be reopened for service soon after the event. The exceptions to the “no collapse” requirement were 750 structures for which the highest level of performance was desirable to protect the substantial investment in these major structures and ensure that they would remain in service after a major seismic event to provide access for emergency responders. The 11 major toll bridges, including the San Francisco–Oakland Bay Bridge, were handled separately because their complexity necessitated a time-consuming dynamic analysis. A risk algorithm was developed for screening of the nontoll bridges. This algorithm was based on four major evaluation criteria: seismic activity, seismic hazard, impact, and vulnerability. Seismic activity was determined by locating structures in one of four fault activity zones, ranked from highly to minimally active. Seismic hazard was determined on the basis of specific conditions (e.g., soil) at the bridge site. Impact was based on such attributes as average daily traffic, route type, and detour length. Vulnerability was assessed on the basis of structural characteristics (e.g., structure type, structure age, presence of expansion joints) to assess the risk to the structure itself. The score on each criterion was multiplied by a weighting factor—seismic activity and hazard were weighted more heavily—and summed with those on the other criteria to arrive at a final score. All 12,600 state highway bridges were processed by using this screening procedure and were prioritized by score. (The 750 major structures were flagged to be in the program.) Additional screening was required for 7,000
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Potential Impacts of Climate Change on U.S. Transportation bridges that failed to meet the minimum performance standard. These bridges were reviewed for specific deficiencies through an examination of the as-built plans for each. The second “paper” screening was used to determine whether the bridge was in the program or retrofit could be deferred; the goal was to make the program more manageable while still addressing the most urgent needs given the available resources. As a result of this second screening, 2,194 bridges were found to be in need of retrofit and were programmed for improvement. A final in-depth field inspection was performed, with the result that some bridges were found to meet the “no collapse” requirement and were removed from the list. A similar procedure was followed for the 12,400 local roadway bridges, resulting in 4,500 structures that required further evaluation and analysis. Since the program was initiated, 2,194 bridges on the state highway system have been retrofit at a cost of $3 billion, and the program is considered 99 percent complete. The remaining phase of the program consists of retrofitting 1,235 bridges on local roadways at an estimated cost of $1.7 billion; the program for local bridges is about 60 percent complete. Funding is provided through a combination of local funds, state gas tax revenues, statewide bond initiatives, and federal funds. Caltrans has maintained ongoing assessment of the seismic retrofit needs of its bridge inventory to identify structures with potential seismic vulnerabilities based on lessons learned since the program’s inception. The bridges identified through this process are prioritized and added to the program as required. State and local governments and private infrastructure providers could adopt a similar approach for identifying and screening critical infrastructure relative to projected climate changes. Key to adopting such an approach is establishing a performance standard for a particular facility that reflects a tolerable level of risk (a “no collapse” equivalent), along with a screening process that takes into consideration such factors as the degree of risk (e.g., magnitude of the hazard), the vulnerability of the facility, and how essential the facility is to the system so priorities for rehabilitation or retrofit can be determined. Source: Information provided by Craig Whitten, Robert Stott, Kevin Thompson, and Cynthia MacLeay, Division of Engineering Services, Caltrans, October 2007.
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Potential Impacts of Climate Change on U.S. Transportation for service soon after the event. The exceptions were 750 structures on state highways and 11 major toll bridges, which were held to a higher standard both to protect the substantial investment in these major structures and to ensure that these vital transportation lifelines would remain in service following a major seismic event to provide access for emergency responders. Second, the experts devised a layered screening system to rate the structures most in need of retrofit; an in-depth physical inventory was conducted only for those bridges that did not meet the performance standard. Finally, elected officials were brought on board, and a combination of funds—federal grants, state gas tax and bond funds, and local revenues—was employed to implement a long-term investment program that continues to this day. State and local transportation officials could adopt a similar approach to assess how climate change may affect transportation assets and develop appropriate adaptation responses and investment strategies. To begin, they might ask the following questions: Which projected climate changes are most relevant for their region? How are climate change hazards likely to be manifested (e.g., flooding, storm surge coupled with sea level rise)? Which transportation assets may be affected? How severe must a hazard be before it becomes relevant and action is required? Can thresholds be identified? How likely is it that a projected hazard will exceed the threshold, when, and where? How much risk can be tolerated, or in other words, what infrastructure performance level is tolerable? What level of investment (capital and operating) is needed to maintain different levels of service? Can acceptable performance standards for all modes of transportation be established? Are there critical levels of service needed to protect health and safety? Who is empowered to make these judgments and decisions? What are the risks of adverse impacts or consequences if no action is taken?
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Potential Impacts of Climate Change on U.S. Transportation BOX 4-2 Decision Framework to Address Impacts of Climate Change on U.S. Transportation Infrastructure Assess how climate changes are likely to affect various regions of the country and modes of transportation (assess hazards). Inventory transportation infrastructure essential to maintaining network performance in light of climate change projections to determine whether, when, and where the impacts of projected changes could be consequential (assess the vulnerability of assets and the system’s resilience to loss of assets). Analyze adaptation options to assess the trade-offs between making the infrastructure more robust and the costs involved. Consider monitoring as an option. Determine investment priorities, taking into consideration the criticality of the infrastructure component as well as opportunities for multiple benefits (e.g., congestion relief, removal of evacuation route bottlenecks). Develop and implement a program of adaptation strategies for the near and long terms. Periodically assess the effectiveness of adaptation strategies, and repeat Steps 1 through 5. If action is necessary, how will investment priorities be determined? Who will make the necessary investments, and how will they be funded? Answers to many of these questions can be found by following the six steps set forth in Box 4-2. This approach provides guidance on how to proceed in addressing many of the technical questions previously posed. However, it does not cover relevant organizational and political issues. Transportation officials must communicate the results of their technical analyses to senior management and elected officials, who make the policy decisions that guide funding choices. In the California situation, the Loma Prieta earthquake focused attention on the need for seismic retrofit of many of the bridges throughout the state to avoid catastrophic failure and loss of life from such an event in the future. With climate changes, however, the impacts will not always be as unambiguously attributable to those
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Potential Impacts of Climate Change on U.S. Transportation changes or as dramatic, with the exception of extreme events (e.g., severe tropical storms, intense precipitation events, heat waves). Thus, communicating the need for early attention to the impacts of climate change requires leadership, supported by compelling analyses, on the part of the transportation community. FINDINGS Climate change poses a complex set of problems, associated risks, and uncertainties with which transportation planners and decision makers are unfamiliar. Among the characteristics of climate change that make it particularly difficult to tackle are uncertainties about the rate and extent of projected changes; the fact that climate change impacts may not follow the modal, jurisdictional, or corporate boundaries of the transportation sector; and the fact that impacts may require coordinated regional or multistate responses that infrastructure providers are poorly configured to address. The significant costs of designing infrastructure to allow for adaptation to long-term climate change impacts in the face of resource constraints, the tendency of transportation planners and engineers to extrapolate from the past and adopt incremental solutions when approaching new problems, and the lack of relevant information and guidance on which to base appropriate actions also affect how transportation planners and engineers view climate change. A change in perspective is needed. First, transportation professionals must recognize climate change as a credible and important problem so that champions will emerge to bring attention to the issue and to make collaboration with climate scientists and meteorologists a priority. Second, addressing climate change requires a longer-term perspective and recognition that investment decisions made today, particularly about the location of transportation infrastructure, help shape long-term development patterns and markets well beyond the 30-year time frames of many public-sector capital improvement plans and private-sector capital budgeting analyses. These decisions also affect how well the transportation system will adapt to climate change in the near and long terms. Third, the significant costs of redesigning, retrofitting, and potentially having to relocate (or protect at great expense) some transportation infrastructure to adapt to potential impacts of climate change suggest the need for more strategic, risk-based approaches to decision making and infrastructure design. Such
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Potential Impacts of Climate Change on U.S. Transportation approaches should be better oriented to assessing the trade-offs between the costs of investments to make the infrastructure more robust and the likelihood and costs of facility failures or major disruptions to the system. The results of such assessments should be presented in a form that can be communicated to senior management and elected officials as a prudent action program, and provision should be made for adjustments as new knowledge becomes available. Finally, addressing the impacts of climate change that require regional and multistate responses is likely to entail developing new coalitions and organizational arrangements. Many of these changes will take time. Fortunately, transportation professionals have many avenues through which to begin to develop adaptation strategies, the topic of the next chapter. REFERENCES Abbreviations IPCC Intergovernmental Panel on Climate Change UNEP United Nations Environment Programme Cambridge Systematics, Inc. 2006. Potential Impacts of Climate Variability and Change to Transportation Systems and Infrastructure—Gulf Coast Study: Long-Range Planning and Investment. Working Paper. Cambridge, Mass., June 30. Deen, T. B. 2006. Preliminary Remarks Outline, Rapporteur. Conference on Climate Change Impacts on U.S. Transportation. Transportation Research Board and Division on Earth and Life Studies, Oct. 12. Dewar, J. A., and M. Wachs. 2006. Transportation Planning, Climate Change, and Decisionmaking Under Uncertainty. Dec. 13. IPCC. 2007. Summary for Policymakers. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, eds.), Cambridge University Press, Cambridge, United Kingdom, and New York. Lockwood, S. A. 2006. Operational Responses to Climate Change Impacts. PB Consult, Dec. 29. Meyer, M. D. 2006. Design Standards for U.S. Transportation Infrastructure: The Implications of Climate Change. Georgia Institute of Technology, Dec. 18. UNEP. 1992. Principle 15. Declaration made at the United Nations Conference on Environment and Development, Rio de Janeiro, Brazil, June 14. Whiteside, K. H. 2006. Precautionary Politics: Principle and Practice in Confronting Environmental Risk. Massachusetts Institute of Technology Press, Cambridge, Mass.
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Potential Impacts of Climate Change on U.S. Transportation ANNEX 4-1 Applying Probabilistic Risk Assessment to Climate Change and Transportation Probabilistic risk assessment (PRA) is a comprehensive, well-developed methodology for evaluating risks so they can be prioritized and managed more effectively. Properly applied, PRA will likely prove an indispensable tool for transportation managers considering the potential impacts of climate change. CLASSIC RISK ASSESSMENT The central idea behind PRA is to define risk as the product of the magnitude of adverse consequences and the probability that those consequences will occur. For instance, the risk of the loss of a coastal road due to a storm surge would be the likelihood of a storm surge rising high enough to inundate the road, multiplied by both the dollar cost of replacing the flooded road and the costs of the economic disruption during the time the road was unusable. In principle, transportation managers could use this risk definition to thoroughly assess the risks posed by climate change for their system. They could list the full range of hazards associated with climate change for their region (e.g., sea level rise, heat) and then estimate the consequences that each hazard, if it occurred, would have for each transportation asset in their region. Each component of this equation has an associated probability. Thus, for example, there is a certain annual probability of occurrence for a 5-foot, 10-foot, or 20-foot storm surge; a certain probability that a road would fail if confronted by a 5-foot, 10-foot, or 20-foot storm surge; and a certain probability that the economic costs of such a failure would be $1 million, $5 million, or $10 million.
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Potential Impacts of Climate Change on U.S. Transportation In sum, the risk due to climate change for all the assets in a manager’s system would be given by where the first term represents the probability densities for each hazard and the second term represents the probability densities for the costs of each hazard (including the probability and the cost of failure) for each asset in the transportation system. Carrying out this analysis would provide transportation managers with an estimate of their total risk and the most important sources of that risk. (In practice, the probability of hazard is time dependent, and any future consequences for long-lived infrastructure would be discounted. However, this simplified expression is sufficient for the discussion below.) Note that the same contribution to risk can be made by a hazard with a relatively high probability of occurrence but moderate consequences and a hazard with a relatively low probability of occurrence but relatively high consequences. Such information provides a solid foundation for determining the most effective ways to manage the risk. CHALLENGES OF ASSESSING THE RISKS OF CLIMATE CHANGE FOR TRANSPORTATION ASSETS AND SYSTEMS In practice, it is difficult to carry out this calculation in its complete form. First, all the necessary data on the likelihood of the various hazards and their economic consequences may not be available. Second, significant uncertainty may be associated with the data that are available. Decision and risk analysts often distinguish between risk and uncertainty. In the former, knowledge of future events can be well characterized by probability distributions. In the latter, decision makers may not view the best available probability distributions as very reliable. For instance, if transportation managers were completely confident that the climate is not changing, they might have high confidence in estimates of the probability of moderate-probability hazards, that is, those expected to occur every 10 years or less as gleaned from weather records for their region extending back several decades or more. Managers might regard estimates of low-probability hazards, that is, those expected to occur every century, as less reliable. However, transportation managers have little basis for
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Potential Impacts of Climate Change on U.S. Transportation assuming that estimates of future climate-related hazards gleaned from past weather records in their region can serve as good estimates of the future likelihood of such events. They need to adjust their expectations on the basis of the results of probabilistic projections from climate models. As discussed in Chapter 2, some hazard estimates from such models, in particular, estimates of the likelihood of extreme events, may be less reliable than others. The final reason that a comprehensive probabilistic risk assessment would prove difficult is that many transportation assets are long-lived, many of the most important impacts of climate change are expected to increase over time, and future transportation managers may take steps that can reduce (or perhaps unintentionally increase) the consequences of future climate changes. To address such changes over time, those who study the impacts of climate change identify four key factors that characterize the ability of a system to adjust to climate change. Using a slightly different language drawn from the ecological and biological literatures as opposed to the engineering literature of formal probabilistic risk assessment, the Intergovernmental Panel on Climate Change defines these factors as follows: Exposure, defined as the manner and degree to which a system is exposed to significant climate variations; Vulnerability, defined as the potential for loss, or the degree to which a system is susceptible to or unable to cope with adverse effects of climate change; Resilience, which refers to the restorative or regenerative capacity of a system when faced with change; and Adaptation, defined as the adjustment made to a system in response to actual or expected climate change to mitigate harm or exploit beneficial opportunities. Exposure and vulnerability are similar to hazards and consequences. System-level resilience is a particularly important concept in the transportation sector because individual assets function as components of a network. The consequences of damage to any one asset will depend on the ability of traffic to reroute by using other routes or modes. They will also depend on the speed with which the affected private transportation providers and public agencies (e.g., state and local governments) can react
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Potential Impacts of Climate Change on U.S. Transportation and bring resources to bear to restore damaged systems to service. The resilience, or lack thereof, of the system can thus reduce or increase the consequences of damage to individual assets in the system. Adaptation will also be an important component of transportation managers’ ability to manage future risks associated with climate change. Managers today do not need to address the full range of potential impacts of future climate change because they can reasonably assume that future managers will take prudent steps to reduce the vulnerability of their assets and increase the resilience of their systems. However, some decisions made today can have implications that might make adaptation actions by future managers significantly more or less effective. For instance, some choices regarding the design and location of new transportation infrastructure may make it easier and less costly for future managers to adapt to climate changes if those changes turn out to be larger than currently expected. If there are two otherwise similar locations for a new road, for example, locating it farther from the coast will make it less costly for future managers to address any vulnerabilities of the asset should sea level rise turn out to be larger than currently expected. CLIMATE RISK ASSESSMENT FOR TRANSPORTATION MANAGERS IN PRACTICE The above factors—lack of complete data, uncertainty about the reliability of projections of future climate change, and uncertainty about the actions future managers will take to reduce the vulnerability and increase the resilience of a transportation system—make it difficult to conduct a comprehensive probabilistic risk analysis for a regional transportation system. In future years, more comprehensive planning frameworks can be expected to come into use that will help transportation managers integrate consideration of exposure, vulnerability, resilience, and adaptation factors. In the near term, however, a number of convenient and relatively simple methods can facilitate transportation managers’ incorporation of these risk assessment concepts into their planning. For instance, the California Seismic Retrofit Program (see Box 4-1) provides an example of a simple screening analysis, based on the concepts of probabilistic risk analysis, that allowed the California Department of Transportation to prioritize seismic retrofit investments for approximately 25,000 bridges on state and local highways. The screening criteria focused
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Potential Impacts of Climate Change on U.S. Transportation on both the vulnerability of individual assets and the resilience of the system. For instance, the program prescribed a higher performance standard for 11 major toll bridges, such as the San Francisco–Oakland Bay Bridge, whose loss would cause major economic disruption and whose replacement would be extremely expensive. Transportation planners can address the potential for future system adaptation by time windows. For instance, operational decisions will be focused on near-term changes in weather and climate conditions, such as more frequent and more extreme events (e.g., intense precipitation and flooding), with which transportation operators are already familiar. Retrofit decisions will determine the performance of assets for several decades and thus should use probabilistic climate forecasts that extend out for several decades to estimate hazards. Finally, land use and location decisions for new infrastructure may influence transportation systems for a century or more, so managers should use probabilistic climate projections for future climate conditions extending into the 22nd century. The decision framework described in Box 4-2 provides one way to incorporate such considerations. ROBUSTNESS AND SENSITIVITY ANALYSIS Particularly when they use multidecadal and century-scale climate projections, transportation managers should pay heed to potentially significant uncertainties in these estimates. In particular, when transportation managers use probabilistic risk assessments to compare alternative design choices or even when they conduct a screening analysis, they should be aware of choices or rankings that are especially sensitive to particular probabilistic estimates. Engineers commonly incorporate safety factors into designs or design standards to account for unforeseen events or abnormal forces on structures. Similarly, transportation managers should recognize that it may be difficult for climate change projections to distinguish a future 100-year storm from a future 500-year storm, or that estimates of the likelihood that sea level rise will exceed 1 m by 2100 may change significantly in the years ahead. To the extent that they can make location decisions and design choices that account for such uncertainties in their risk assessments, today’s transportation managers will help future stewards of their systems minimize avoidable surprises.