The Road to Resilience
Addressing Transportation Infrastructure Vulnerability
As transportation departments across the country deal with the pressing challenges of growth, development and aging infrastructure, one agency in Maryland is expanding that focus to include resiliency.
By Amy Krebs, Ruby Shamayleh, PMP, and Elizabeth Habic
IMAGES COURTESY STANTEC
Most scientists agree that the impacts of climate change have already begun. Increases in temperature have given way to sea level rise, precipitation intensity and extreme weather events. According to the 2014 National Climate Assessment, the climate change trends described in its 2009 report have occurred and further evidence has only strengthened confidence in the conclusion of a warming trend.
States, cities and towns are on the front lines in responding to this multi-faceted dynamic. While many agree that the time to act is now, there is no universally accepted plan of attack. Just as the impacts of climate change vary, so too must the response of public agencies as they move to protect and strengthen their communities.
Maryland is one of states most vulnerable to climate change due to its exposure to the Atlantic Ocean, Chesapeake Bay, and numerous tidal and non-tidal rivers. The Maryland State Highway Administration (SHA) has taken proactive measures to better understand the potential impacts of climate change that may hold lessons for others.
In 2013, SHA initiated a pilot study to assess the vulnerability of select transportation assets to climate variables or stressors; to develop engineering approaches to address current and future climate induced risks; and to make recommendations for policy or process changes to improve the resiliency of Maryland’s highway system. The study was funded in part by a grant from the Federal Highway Administration and utilized the agency’s Climate Change & Extreme Weather Vulnerability Assessment Framework.
The pilot study was a collaborative effort. SHA provided supported monthly working group meetings and larger engineering workshops. The Salisbury University Eastern Shore Regional GIS Cooperative provided predictive models. Stantec Consulting Services Inc. served as the prime consultant for the study and for the preparation of the final report.
Data was first reviewed in SHA’s Asset Management Database, which proved a key component in assessing vulnerability. Asset information was compiled from a variety of sources, including the Maryland Department of the Environment Bridge and Culvert Survey Database and the Federal Emergency Management Agency’s National Flood Hazard Layer GIS service. Hazus-MH 2.1 and Flood Depth Grids for 10-year to 500-year floods were used for precipitation estimates for the 2050 and 2100 sea level change projections.
In many cases, existing state or regional information, such as the 2013 report, Updating Maryland’s Sea Level-Rise Projections, formed the foundation of these analyses. To maximize the assessment of the study area, SHA chose to update data with more site specific information. The augmented data came from higher resolution LiDAR surveys and future climate projections generated by the Coupled Model Inter-comparison Project Climate Data Processing Tool, which was used to project changes in precipitation and temperature conditions.
Two primary assets were evaluated: bridges and roadways. Each of the climate variables were reviewed and evaluated for their potential impacts on these transportation assets. Because flooding is a current issue the region faces, the team focused on sea level change, storm surge from extreme weather events, and increased precipitation intensity.
SHA is responsible for a large number of assets, from the Atlantic Ocean to the Alleghany Mountains. Some of these assets will be more impacted by climate stressors related to flooding than others.
In order to conduct a detailed study of all roads at the county level, SHA conducted a Tier 1 initial asset screening. This screening used digital maps and GIS data to identify exposed assets. That limited the evaluation only to those assets at risk.
The Tier 1 initial screening datasets included the 2100 Mean Higher High Water sea level change projections; Sea, Lake and Overland Surges from Hurricanes models for a Category 3 hurricane; and Federal Emergency Management Agency 100-year floodplain boundaries. By combining the outer limits of these data layers, a Climate Change Impact Zone was developed.
Next, the team performed a Tier II analysis on the assets identified in the screening for two geographically distinctive counties: Anne Arundel and Somerset.
The counties were chosen because their location and exposure to the climate stressors represented two different scenarios within the state. The Tier II analysis evaluated in more detail the assets within the Climate Change Impact Zone using the newly developed Vulnerability Assessment Scoring Tool (VAST). A Microsoft Excel-based analytic tool, VAST uses key asset information such as bridge age, climate data and other vulnerability indicators including the current frequency of flooding to develop a composite vulnerability score. The weighting factors were based on expertise drawn from similar studies and refined through an iterative process. The scores that VAST generates then are broken down into three components: asset exposure, sensitivity and adaptive capacity.
The study also developed a methodology called the Hazard Vulnerability Index (HVI), which compares the risk value for road segments vulnerable to the chosen flood-related climate change stressors. The equation for calculating the HVI risk value is comprised of three components: evacuation route designation, functional classification, and projected flood depth.
ANALYZING THE RESULTS
Flood inundation modeling identified road segments at risk to permanent inundation from sea level rise. The HVI then provided a risk value for those road segments exposed to each of the climate stressors evaluated: sea level rise, storm surge and precipitation. For the HVI assessment, road segments were categorized as Critical, High, Moderate, or Low Risk. These categories were based on the risk value and are in reference to the modeled flood depth associated with sea level rise, precipitation and storm surge, as well as the functional classification and evacuation route designation for each roadway.
To highlight the roadways most at risk and to allow for a similar comparison with the VAST bridge analysis output, the roadways most at risk in 2050 and 2100 were presented in list format, itemized according to those with the most mileage within the Critical, then High Risk categories. Bridge structures that were vulnerable to the identified three climate stressors for the years 2050 and 2100 were listed based on the vulnerability scores calculated in VAST. The location and asset identification of the most vulnerable structures were depicted on maps. Tables presented the sum of weighted averages of all the vulnerability components of the structures.
Due to the inter-relationship of the bridges and roads, the two assets were evaluated together to identify the geographic areas with the highest level of vulnerability. These geographic areas were identified as Vulnerable Areas at Risk.
LOOKING TO THE FUTURE
SHA will use the methodology developed in the study as a framework to steer actions regarding its transportation assets. The study specifically established a framework for assessing vulnerability and prioritizing assets, while providing guidance on adaptive measures to make the transportation system more resilient to impacts of climate change and extreme weather events.
Through the marked involvement of SHA staff, the study also has served to increase awareness of the potential impacts of climate change and the strong need for asset adaptation. By looking to the future, Maryland is addressing its transportation infrastructure vulnerability today.
Elizabeth Habic is Team Leader, Environmental Planning Division, Office of Planning & Preliminary Engineering, Maryland State Highway Administration; ehabic@sha. state.md.us.