The Tennessee Department of Transportation is responsible for building and maintaining much of the state’s transportation infrastructure. Following a number of extreme weather events, the Tennessee Department of Transportation (TDOT) recognized that the agency’s management of those assets required methodological approach to assess the vulnerability of the state’s transportation network.
In May 2010, Nashville, Tennessee experienced a 1,000-year flood event, causing 21 deaths in Tennessee and widespread property damage. In 2013, there were severe weather-related problems on the Cumberland Plateau, in the eastern part of the state. Rockslides blocked traffic in areas lacking alternative transportation routes. In other regions, sinkholes opened on interstate highways.
These types of extreme events prompted TDOT officials to conduct a statewide vulnerability assessment for its transportation infrastructure as a first step in identifying cost-effective approaches to increasing the resilience of the system. The assessment took advantage of a pilot program offered by the Federal Highway Administration (FHWA).
FHWA has funded a series of studies across the country to begin increasing the resiliency of the country’s transportation infrastructure in the face of increasingly frequent and severe weather events. The first round of FHWA pilot projects validated a general approach to conducting an extreme weather vulnerability assessment. They focused primarily on coastal locations where many of the risks were related to storm surge and sea level rise. FHWA’s second round of pilots, although also primarily focused on coastal states, included inland states, and Tennessee became the first inland state to perform a statewide vulnerability assessment.
TDOT is now trying to integrate the results of the screening-level, statewide vulnerability assessment into TDOT’s planning, management and operational policies, according to Alan Jones, Policy Manager, Long Range Planning Division at TDOT. The agency’s assessment has been an important screening tool to identify critical transportation assets, better understand extreme weather risks, and identify specific assets that warrant a more detailed analysis.
FHWA Vulnerability Assessment Framework and Tennessee’s Approach
The Tennessee project developed an approach to the vulnerability assessment that was based on FHWA’s Vulnerability Assessment Framework, while also taking into account the unique characteristics of Tennessee and its transportation system. The approach involved identifying critical transportation assets, defining the types of extreme weather events that could occur while taking into consideration expected changes in certain climate variables, assessing the damage potential and resilience of the transportation assets when impacted by the extreme weather event, and combining this information to reach conclusions about the vulnerability of the asset.
To manage the number and range of transportation assets statewide, TDOT’s first step was to group its transportation assets into generic asset categories. The categories included roads, rail lines and rail yards, navigable waterways, ports, bridges, airport runways, pipelines, transit systems, and more. It was not possible in this initial screening study to differentiate the unique characteristics of specific facilities, such as pavement binder or age of asset.
Criteria for determining the criticality of an asset included the volume of activity, the asset’s strategic importance, the existence of redundant capability, the asset’s use for emergency response, and local knowledge of the importance of the asset.
The range of extreme weather events and climate change to be expected in Tennessee was based on analysis of information from the National Weather Service and well-tested global climate models. The types of weather events included were extreme temperatures (both high and low), heavy rain, drought, strong winds and tornados, ice storms, and major snowfalls. Trends in the data identified which counties were most likely to see increased severity and frequency of extreme events. The climate data also identified counties that can expect the most significant changes with respect to projected temperature and precipitation.
The process of assessing damage potential and asset resilience was performed through a statewide survey conducted of transportation stakeholders, such as government agencies, freight carriers, transit service providers, airport authorities, and shippers.
The survey results painted a picture of tremendous variation in vulnerabilities across Tennessee. Key findings included:
- Wind and flooding are by far the events of greatest concern across the state, potentially affecting multiple classes of transportation assets. For example, there is significant risk from flooding in Memphis. Moreover, wet ground and strong winds could produce large numbers of tree falls and utility poles across roads, severely restricting movement.
- Movement of vessels, including barges carrying coal and other products, on Tennessee rivers can be disrupted by extreme weather. Locks are vulnerable to flooding and river levels that allow barge traffic are vulnerable to extended periods of high temperature and low rainfall.
- Rockslides in middle and eastern Tennessee could substantially disrupt transportation networks in areas with limited alternate routes.
- With the exception of one county, winter weather is a less significant concern.
Next Steps for TDOT
TDOT plans to take a number of steps to implement the results of its vulnerability assessment.
The agency plans to follow-up with TDOT’s four regions to communicate the results of the study. This will include developing regional “briefing books” to condense the study and communicate specific vulnerabilities so they can be easily understood and quickly referenced. These briefing books will be tailored to each of the four TDOT regions to account for differences across the State and to make the information more useful to local and regional planners. The agency also will select up to 20 of the state’s most vulnerable assets for more refined, targeted analyses, including development of potential adaptation strategies.
In addition, TDOT will incorporate information from the screening-level vulnerability assessment as it develops its risk-based transportation asset management plan (TAMP) required under the Moving Ahead for Progress in the 21st Century Act (MAP-21).
TDOT will also consider additional tasks in following up on the vulnerability assessment.
- TDOT has already identified slopes near roadways that are most vulnerable to rockslides, TDOT will combine this information with the data regarding locations of expected increased precipitation, to help select priority sites for potential slope stabilization projects.
- Based on the more detailed assessment of critical transportation assets, TDOT will identify additional adaptation projects for possible addition to the State’s Transportation Improvement Program (TIP. TDOT would need to determine how to evaluate adaptation projects against congestion relief projects. This would likely require quantifying the benefits of implementing adaptation projects.
- TDOT will consider issues associated with whether and how to modify repair and replacement standards so that facilities may be upgraded to a more resilient condition.
- Developing linkages throughout TDOT and with other transportation agencies (e.g., MPOs) to address extreme weather more effectively.
Lessons Learned and Advice to State DOTs
A statewide vulnerability assessment is an ambitious project and required a significant commitment of time and resources; however, the project results served as a vital screening tool that can be used to determine where best to focus a more detailed study to determine what, if any, adaptation measures might be warranted. For example, the statewide study required grouping assets into classes, such as “roads,” but this approach has substantially limited the number of roads in the state that warrant a further review, a review which will allow more unique characteristics of the asset to be evaluated to determine vulnerability, such as pavement binder, age of the road, and more.
Another lesson learned is the importance of local stakeholder knowledge and input. The project conducted regional meetings across the state and were able to get a much better understanding of what assets and routes are considered critical, or not, from a local perspective. Local knowledge of how assets perform during extreme weather events was also vital to the study. TDOT field staff already have a great deal of knowledge of regional vulnerabilities that were relevant to the study.
For more information, contact Alan Jones, Tennessee Department of Transportation at [email protected].