Assessing Vulnerability and Risk of Climate Change Effects on Transportation
Infrastructure: Pilot of the Conceptual Model
This document outlines a conceptual Risk Assessment Model that will be piloted by three to four State
Departments of Transportation (DOTs) or Metropolitan Planning Organizations (MPOs) (hereafter, “transportation
agencies”) selected by the Federal Highway Administration (FHWA). Using feedback and lessons learned during
this pilot phase, FHWA will refine this draft conceptual model and develop a final version for all transportation
The goal of the Risk Assessment Model is to help transportation decision makers (particularly transportation
planners, asset managers, and system operators) identify which assets (a) are most exposed to the threats from
climate change and/or (b) could result in the most serious consequences as a result of those threats. Assets in this
context refers primarily to infrastructure assets (such as bridges and roads), but could include other assets that
benefit the transportation system such as a coastal wetland buffer.
The conceptual model consists of three primary components, as shown in :
1. Develop inventory of assets;
2. Gather climate information; and
3. Assess the risk to assets and the transportation system as a whole from projected climate change.
Inventory of Assets Climate Information
Existing Develop inventory
inventories of assets
What is the likelihood
How important Less Low likelihood/ and magnitude
is each asset? important Low magnitude of future
Monitor and revisit
as resources allow
High likelihood/High magnitude
High likelihood/Low magnitude
Risk Low likelihood/High magnitude
Is the asset
High or medium
What is the Within scope of
What is the Risk Assessment pilot
future stressors will
of the impact
measurably impact Outside of scope of
on the asset?
the asset? Risk Assessment pilot
Monitor and revisit What is the Identify, analyze, and prioritize
Low risk medium
as resources allow integrated risk? risk adaptation options
Figure 1: Structure of the conceptual Risk Assessment Model that will be piloted by State DOTs and
Each of these components is described in more detail below. The conceptual model is intended to be broad and
flexible in how it is applied. FHWA will provide limited support to the selected transportation agencies to
implement the model, and will collect feedback and lessons learned; this information will feed into a revised
version of the model.
Asset Inventory and Prioritization
Develop Inventory of Assets
Transportation agencies selected for the pilot will first compile an inventory of all assets they wish to evaluate
during this pilot phase. Example asset categories are
provided below, although each pilot area should select Box 1: Example Criteria for Identifying Important Assets
asset categories that correspond to their planning priorities. The DHS National Critical Infrastructure Prioritization
When compiling this inventory, agencies should also gather Program (NCIPP) uses consequence-based criteria to
any information that may help to later evaluate how identify national critical infrastructure. Capacity-based
resilient the asset is to climate stressors, and how costly criteria can also indicate the importance of assets.
damage to the asset could be. Example information types Examples of consequence-based criteria include:
are provided below. • Loss of life,
• Economic costs,
This inventory should include, but not be limited to, all
• Ability to re-route, and length of detour, and
assets that fall under the selected asset categories. Existing
state and MPO inventories of assets will be the primary • Time to rebuild if damaged.
source of this information. FHWA understands that Examples of capacity-based criteria include:
inventory datasets may not be available in all cases, and • Annual average daily traffic volume,
that some data compilation may occur during this pilot • Ridership (mass transit), and
study, although data collection is outside of the scope of • Span or tunnel length.
this Conceptual Risk Assessment Model.
FHWA will also work with the agencies to identify potential sources of relevant data. National databases, such as
those identified in the Appendix, can serve as a starting point for inventory development; state and local agencies
may have more comprehensive records and knowledge of assets beyond what is included in national datasets.
FHWA is interested in feedback on which datasets could be used in this step, and which ones the agencies found
Example Asset Categories Example Information Types
• Bridges and tunnels • Age of asset
• Key road segments (and evacuation routes) • Geographic location
• Rail (passenger and freight) • Elevation
• Transit system assets • Current/historical performance and condition
• Port and airport assets • Level of use (traffic counts, forecasted demand)
• Signals and traffic control centers • Replacement cost
• Back-up power, communication, fueling, and other • Repair/maintenance schedule and costs
emergency operations systems • Structural design
• Intelligent Transportation Systems (ITS), signs • Materials used
• Pipelines • Design lifetime and stage of life
• Wetlands • LIDAR (Light Detection And Ranging) remote sensing
• Floodplains data
• Vegetative Cover • Federal Emergency Management (FEMA) maps
• Vegetation survey
How Important is Each Asset?
Transportation agencies should initially “screen”
the assets located in their jurisdiction based on the Box 2: Resources for Climate Data
relative importance of each asset. Using existing Historical Data
priorities and metrics (such as traffic flow,
Historical weather and climate data are available from the NOAA National
emergency management, movement of goods), Climatic Data Center:
agencies should consider which assets are most
important for meeting those priorities. • Comprehensive U.S. climate data available at:
• U.S. climate maps available at:
Many transportation agencies have existing
evaluation tools or guidelines they use to prioritize
• Other State or Local weather and climate data may be available.
assets for maintenance or repair. For example,
after a snowstorm, how are roads prioritized for Projected Data
snow removal? Other criteria used to prioritize Transportation agencies can use the Climate Change Effects Report
assets could include the level of usage (annual developed by FHWA as a starting point for understanding future climate.
average daily traffic), class (local road versus Agencies may want to supplement this information with sources of local or
regional data and/or input from climate change experts familiar with state and
arterials), ownership (a road is privately owned,
regional climate details.
and not under the entity’s jurisdiction), the
importance of an asset within the larger Data sources that have projections of future climate change from many
transportation network (including potential for different models for various emissions scenarios include:
adverse network effects), its value in emergency • Statistically downscaled data from the World Climate Research
situations (e.g., for evacuation), and/or Programme's Coupled Model Intercomparison Project phase 3 (CMIP3):
redundancy. The loss of a particular asset may http://gdo-dcp.ucllnl.org/downscaled_cmip3_projections/
have ripple effects throught the network that
make an asset important to include in the Risk • Dynamically downscaled data from the North American Regional
Assessment Model. Box 1 describes “consequence- Climate Change Assessment Program (NARCCAP):
based” and “capacity-based” criteria used by the
• A new project funded by USGS is developing a comprehensive web-
Department of Homeland Security (DHS) to based dataset of high-resolution (downscaled) climate change
identify national critical infrastructure and provide projections for the entire U.S.
asset prioritization guidance to states and territories. During this pilot phase, FHWA is interested in how assets are
currently prioritized by transportation agencies when making decisions related to safety, reliability, mobility,
emergency management, and ultimately, climate change. To streamline the process, agencies should initially set
aside “less important” assets, and then revisit them later if resources permit; see “Monitor and Revisit as
Resources Allow” for more information.
Gather Climate Information
As agencies develop their asset inventory, they will also gather local- or regional-level information on past changes
and projections of future climate. Agencies should use this information to assess impact. In later steps, FHWA may
assist agencies in using this information to translate projected climate changes into tangible climate-related
impacts on the transportation system. Agencies should revisit this step as new information becomes available.
Historical climate and weather information will provide clues as to how assets may withstand future climate
stressors. Projected climate information, is important for estimating future climate conditions to plan for. Both of
these types of information will be used later in this risk assessment.
What is the likelihood1 and magnitude of future climate changes?
In this document, “likelihood” refers to the general probability of occurrence and is used preferentially over the term “probability,” because it
colloquially denotes a probability range, rather than a single value. As discussed in the climate assessments from the Intergovernmental Panel
Each climate dataset will have associated
uncertainties2. Uncertainties are generally Box 3: Risk Assessment of Bridge Assets – An Example
smaller with observational data than with Transportation agencies already document, prioritize, maintain, and repair
bridge assets using tools that can assist with this conceptual Risk Assessment
projections of future climate conditions. The
model. This example shows how the National Bridge Inspection Program
range of uncertainty associated with future (NBIP) could be used.
projections has been characterized for major
U.S. regions in the Climate Change Effects 1. Use existing information required by the NBIP to develop an initial
inventory of bridge assets, including other non-highway bridge assets
Report developed by FHWA using available regional, state, and local records.
Consider data such as average daily traffic, length/width of bridge, scour
criticality, and the bridge’s sufficiency rating to assess the importance of
each bridge according to consequence- and capacity-based criteria (see
Box 1) or other state or regional priorities.
2. Once less-important bridge assets have been screened, assess the risk
to the remaining assets. First, assess the vulnerability of each asset to
climate impacts. Consider the following vulnerability assessment
examples for bridge assets:
a. Analyze previous bridge failures resulting from weather events;
b. Identify current weather-related stressors and their impact on bridge
performance using bridge inspection reports and maintenance records;
c. Identify scour-critical bridges; evaluate their performance, and
d. Review weather-related specifications that are already incorporated
into bridge design. For example, design flood and storm frequency
(e.g., 50-, 100-, or 500-year frequencies), drainage, and material
e. Of those assets with a low vulnerability to current climate impacts,
review projected climate changes to identify those assets that could
become vulnerable to future climate impacts.
Assets with low vulnerability to projected climate effects should be
monitored and reassessed as resources permit.
3. For assets with a medium or high vulnerability, evaluate the likelihood of
measurable impacts in the future.
Assets can be sorted into high- and low-likelihood categories. For example,
bridges with historical drainage problems, overtopping, or scour-critical
bridges may be assessed with a high likelihood of impacts from sea level
rise, storms, and/or increased precipitation.
Consider cumulative effects. Heavier rainfall coupled with sea level rise may
not only increase the risk of flooding, but may also increase scour and
weaken embankments and bridge supports.
4. Next, assess the consequence of impacts on each asset. Consequence-
and capacity-based criteria that were used to screen less-important
assets can be applied at this step to each type of climate impact. Assets
should be categorized into high- and low- consequence groupings.
Finally assess the risk to each asset by group assets by high/low likelihood and
http://www.fhwa.dot.gov/hep/climate/climate_effects/index.cfm (see Box 2). There are several sources of
uncertainty in projections, including: (1) uncertainties with physical processes and their representation in global
and regional climate models; (2) uncertainties with future greenhouse gas emissions; and (3) the stochastic and
on Climate Change and the U.S. Global Change Research Program, it is generally not possible to assign a single integer of the percent probability
to a particular future climate effect.
“Uncertainty” is an expression of the degree to which a value (e.g., the future state of the climate system) is unknown. In general terms,
uncertainty can result from lack of information or from disagreement about what is known. (From IPCC, 2007, Glossary of Terms.
unpredictable aspects of the climate system. Therefore, it is important to consider a range of future climate
scenarios, such as done by the Climate Change Effects Report. The larger the range of uncertainty, the smaller the
likelihood that the mean of the projected range will be near the actual future value. Thus, in the absence of explicit
likelihood information for a particular variable, the range of uncertainty may be used to approximate the
A screening analysis should be conducted at this stage to set aside potential climate change effects that are both
relatively uncertain (e.g., the sign of the change is unknown) and small in magnitude. These potential effects may
be revisited at a later time. Potential changes that should not be screened out at this stage are those that are
relatively uncertain but possibly large (e.g., changes in hurricane characteristics), and those that are relatively
certain but small in magnitude (e.g., regional temperature changes). Judgments about the significance of the
magnitude will be subjective since a change in one climate variable may be significant to one region or
transportation mode, but insignificant to another. FHWA will work with the agencies to provide guidance on how
to take uncertainty and magnitude into account.
Risk is the potential for an unwanted outcome resulting from an event—in this case, a climate stressor. It is
determined by the product of: (a) the likelihood of the impact; and (b) the consequence of the impact.3 The
likelihood of an impact is, in part, a function of the likelihood of the climate stressors. It is also a function of the
vulnerability of the transportation element to climate change. Vulnerability also affects the magnitude of the
In this phase, agencies will: (1) screen assets that are less vulnerable to projected climate effects; (2) assess the
likelihood of a particular impact resulting from a defined set of stressors, (3) assess the consequence of the impact,
not just in terms of what it does to a particular asset, but in terms of how it affects the surrounding community
and beyond, and (4) assess the integrated risk of the consequence and likelihood.
What is the vulnerability of the asset to projected climate change?
Assess vulnerability using historical weather information
By understanding how weather events had previously affected an asset, transportation agencies will be better able
to understand how weather events in the future may affect that asset, or similar assets. Furthermore, historical
experience may provide information on the significance of the impact to the transportation system if a certain
asset is damaged or destroyed.
To address this question, agencies should consider the historical performance of assets during specific weather
events. For example, agencies could consider:
• the repair costs or retrofits caused by past weather events,
• budgets and spending for services that respond to weather events (e.g., snow plowing),
• effects of past weather events on services provided by an asset (e.g., changes in VMT, the value of the
goods transported), and
• role of the asset in emergency response and evacuations required in past weather events.
By comparing historical weather events with historical maintenance and repair needs, agencies can estimate how
well specific assets withstand certain climate stressors. In doing so, they may be able to identify physical or
environmental characteristics that make a structure more or less vulnerable to a given climate stressor. If a
specific climate stressor does not appear to have a significant effect on a given asset, agencies may screen that
climate stressor-asset combination from the assessment, record it, and revisit it as resources allow.
As defined by the Department of Homeland Security in its 2009 National Infrastructure Protection Plan. See
www.dhs.gov/xlibrary/assets/NIPP_Plan.pdf, p. 27.
Each agency should identify information sources that could be consulted or compiled to evaluate the effects of
current climate stressors on assets, and will assist agencies in identifying climate stressors that are already taken
into account in the design, operation, and maintenance of existing assets.
Assess whether future climate change introduces additional climate vulnerability
At this point, agencies will have a good sense of how well assets can withstand specific climate stressors, many of
which may be present (and perhaps be more/less frequent) in the future. However, projected climate scenarios
may include stressors to which assets are currently not exposed. For example, climate projections may indicate
that an asset will likely be exposed to extreme temperatures not previously experienced. The projected extreme
temperatures may exceed certain thresholds at which the asset material is compromised. Or, some assets may
have been exposed to temporary flooding, but projected climate information may indicate longer-term inundation,
which can have very different impacts on an asset. Finally, agencies must consider the cumulative impacts of more
frequent climate stressors; a particular asset may be able to withstand the first and second flood (for example) but
not the 20th flood.
Figure 2 illustrates the classification of risks to an asset according to categories of likelihood and consequence.
What is the likelihood of a particular impact resulting from a defined set of stressors?
Agencies will need to apply climate projections to evaluate the likelihood of future impacts, including cumulative
effects from changes in several climate stressors. To the extent that information is available, impacts will be split
into high- and low-likelihood groupings. Transportation agencies will have the flexibility to define what a “severe”
climate effect means for them, and effects that are determined to be less severe can be recorded and revisited as
resources allow. Projected changes in climate that are so uncertain that it is not possible to determine whether
future stressors will measurably impact the asset can also be set aside and revisited later.
What is the expected consequence of the impact on society?
When an asset sustains a particular impact, what is the consequence to society? Transportation agencies may
wish to consider the level of use of an asset, the degree of redundancy in the system, or the value of an asset (in
terms of cost of replacement, economic loss, environmental impacts, cultural value, or loss of life) to determine
consequence. FHWA will assist in categorizing assets into high- and low-consequence groupings.
This step will take into account the criticality assessments conducted earlier. Transportation agencies can use the
criteria listed in Box 1 as a starting point for assessing the consequences of an impact. Approaches that are
currently used by transportation agencies to define and prioritize important system components may help identify
high-consequence assets. For example, approaches and metrics are used to determine road maintenance and
construction priorities. FHWA is interested in determining what approaches already exist.
Transportation agencies may have models, computer software, or other methodologies available to them to assist
in identifying consequences of changes in climate. For example, the American Association of State Highway and
Transportation Officials (AASHTO) is currently testing a new pavement design model (the Mechanistic-Empirical
Design of New and Rehabilitated Pavement Structures) that will allow input of alternate climate scenarios to
determine how pavement will hold up under those conditions. Analyses including environmental assets can help
determine how environmental conditions may alleviate impacts to infrastructure assets.
What is the integrated risk of climate change to the asset?
For assets deemed “vulnerable”, the integrated risk assessment
for an asset should jointly consider the likelihood that the asset Box 4: Proactive and Opportunistic Adaptation
will experience a particular impact, and the consequence of that Measures – An Example
impact on the surrounding community or region (from a Problem: Extended periods of extreme heat can impact
the integrity of pavement, causing softening and rutting.
health/safety, economic, environmental, cultural, or other point
Opportunistic options might include:
of view). Assets that have a low likelihood of being impacted by
• Enhancing existing maintenance operations (e.g.,
future climate and a low consequence of that impact occurring
increasing the frequency of maintenance, milling
will be screened, recorded, and revisited as resources allow. The out ruts), and
remaining assets, grouped according to high/low likelihood and • Retrofitting roads with rut-resistant asphalt at
high/low consequence of impact, is the outcome of the Risk scheduled maintenance periods.
Assessment Model. As a result of this analysis, agencies will have Proactive options could involve:
a prioritized list of assets at risk from future climate change • Developing new, heat-resistant paving materials,
impacts, developed according to their own criteria. The • Overlay existing roads with more rut-resistant
integrated risk is often represented by a two-dimensioned asphalt, and
matrix that classifies risks into three categories (low, moderate, • Abandoning roads before the end of their
high) based on the combined effects of their likelihood and expected service life.
consequence. An example matrix from the 2006 FHWA Sources:
document Risk Assessment and Allocation for Highway Climate Change Science Program (CCSP). 2008.
Construction Management is provided in Figure 2 Impacts of Climate Change and Variability on
Transportation Systems and Infrastructure: Gulf
Coast Study, Phase I. Washington, DC: Department
Monitor and Revisit as Resources Allow of Transportation.
NRC. 2008. Potential Impacts of Climate Change on
At various points in the conceptual model, transportation U.S. Transportation. Transportation Research Board
agencies will apply screens to separate (i) less-important assets, Special Report 290. Washington, DC: Transportation
(ii) unlikely and low-magnitude changes in climate, (iii) less- Research Board.
vulnerable assets, and (iv) vulnerable assets facing a low integrated risk of climate change, according to their own
existing methods and priorities. These screens will help prioritize assets according to vulnerability and
consequence, based on the most current and relevant data available.
These screens are important to apply and document so that agencies have the option of revisiting and re-
classifying assets. Changes in asset inventories, refinements in future climate projections, and improved
understanding of the relationships between changes in climate, asset vulnerability, and infrastructure and
environmental assets may alter categorization of some assets in future years. FHWA is interested in tracking the
elements that have been initially set aside, and in identifying monitoring mechanisms—either existing or potential
—that can be used to evaluate whether such assets should be revisited, depending upon available resources.
Agencies may also identify elements where data is unavailable, or the impacts and/or consequences of future
climate changes are unknown and cannot be assessed. It may be important to also monitor and revisit these
assets, climate changes, stressors, and impacts once more data is available. Tracking these elements for
monitoring can also help agencies set priorities for data collection and research as resources are available.
Next Steps: Identify, Analyze, and Prioritize Adaptation Options
At the conclusion of this pilot, transportation agencies should have identified the assets that are most critical to
their transportation priorities, and most at-risk to climate change. The ultimate purpose of identifying these
critical vulnerable assets is to inform decisions on how to prepare for and adapt to climate change. Although not a
part of this conceptual model, the next step involves making decisions about what to do about the risks that
climate change poses to the transportation system.
This step will eventually help transportation agencies identify risk reduction options (adaptation strategies) for
assets that scored either medium or high risk based on an integrated assessment of likelihood and consequence.
Although identifying and implementing adaption options is not included in the pilot program, adaptation measures
can occur in two timeframes:
1. Opportunistic adaptation measures, or measures that take advantage of scheduled or necessary
equipment planning, maintenance, repair, or end-of-life cycles to respond to identified risks from future
2. Proactive adaptation measures, or measures that are implemented before scheduled or necessary
equipment planning, maintenance, repair, or end-of-life cycles to prevent impacts from climate stressors
Not all adaptation measures are proactive, as shown in the example in Box 4. The benefits of opportunistic
measures are that they can be integrated with existing activities that are already being undertaken. For
transportation agencies with constrained budgets and limited resources, implementing adaptation options
opportunistically at planning or budgeting stages, intervals of maintenance or repair, and at the end of life of
assets can be less costly than pursuing options proactively.
Appendix 1: Existing Resources that can Assist Transportation Planners in
Evaluating the Risks and Vulnerability from Climate Change Effects on
FHWA recognizes that the best, most comprehensive data for developing inventories and assessing the risk and
vulnerability of assets often exist at regional, state, and local levels. At the same time, datasets and guidelines exist
at the national level that can serve as a good starting point for developing inventories. These resources can serve
to help identify data elements that agencies may wish to collect on their assets.
Databases, guidelines, and other resources identified at the national level that can help build asset inventories are
listed below. This is not a comprehensive list, but provides examples of the resources that are available for various
transportation infrastructure types. During the pilot phase, FHWA is interested in hearing feedback on which of
these sources are particularly useful, as well as which resources should be added to this list.
Existing National Databases and Tools that can Assist in Developing Asset Inventories
• Federal Highway Administration:
o FHWA Highway Statistics (highways)
o Long Term Pavement Performance DataPave Online (road surfaces)
o National Bridge Inventory (bridges)
o Highway Tunnel Inventory (tunnels)
o Major Tunnel Projects (tunnels)
• U. S. Geological Survey:
o National Bridge Scour Database (bridges)
• Bureau of Transportation Statistics:
o National Transportation Statistics (transportation system)
• Federal Emergency Management Agency:
o Hazards U.S. Multi-hazard assessment tool (HAZUS-MH) (infrastructure)
Existing Design Guidelines that can Assist in Assessing Risk and Vulnerability from Climate Change Effects on
Transportation Infrastructure or other resources.
• American Association of State Highway and Transportation Officials (AASHTO):
o Highway Drainage Guidelines, Volume III, Erosion and Sediment Control in Highway Construction
o Guide for Design of Pavement Structures and 1998 Supplement (pavement and road surfaces)
o A Policy on Geometric Design of Highways and Streets (5th ed.) (highways)
o AASHTO Model Drainage Manual (3rd ed.) (drainage)
o Manual for Bridge Evaluation, First Edition (bridges)
o AASHTO Load and Resistance Factor Design (LFRD) Bridge Design Specifications with 2008 and 2009
Interim Revisions (4th ed.) (bridges)
• Federal Highway Administration:
o Evaluating Scour At Bridges, Fourth Edition. FHWA Circular No. 18 (bridges)
o Highways in the Coastal Environment (2nd ed.). Hydraulic Engineering Circular 25 (bridges)
o Integrating Climate Change into the Transportation Planning Process
o Technical Manual for Design and Construction of Road Tunnels - Civil Elements, available at
o Road Tunnel Design Guidelines, available at http://www.ntis.gov/search/product.aspx?
• Transportation Research Board (TRB)
o TRB Superpave Committee, Superpave: Performance By Design, Final Report of the TRB Superpave
Committee, available at:
(pavements and road surfaces)
• National Cooperative Highway Research Program (NCHRP)
o NCHRP 1-37A: Guide for Mechanistic-Empirical Design of New & Rehabilitated Pavement Structures,
available at http://onlinepubs.trb.org/onlinepubs/archive/mepdg/home.htm (pavement and road
• The Asphalt Institute:
o State Binder Specs Database (road surfaces)
For more information, contact: Faiz Khan 202-366-5843 Faiz.Khan@dot.gov or Mike Culp 202-366-9229 Michael.Culp@dot.gov