Projected changes in climate conditions and increasing instances of extreme weather events have become an ongoing challenge for transportation agencies charged with ensuring the long-term safety and functionality of surface transportation systems. According to the 2014 National Climate Assessment, in the coming decades “all regions and modes of transportation will be affected by increasing temperatures, more extreme weather events, and changes in precipitation.”
Current and future climate impacts that may affect transportation systems include rising sea levels, increased precipitation in some areas and decreased precipitation in other areas, higher risk of drought and wildfires, stress on ecosystems, and greater risk of flooding.
While infrastructure in coastal areas is particularly vulnerable to sea level rise, storm surge and flooding, inland states also are facing increasing impacts from extreme events, including riverine floods, winter storms, wildfires, and landslides.
Impacts to infrastructure include buckling of pavement from heat or freeze-thaw conditions; damage to culverts and roads, tunnels, bridges and transit systems from flooding, landslides, and erosion; inundation of infrastructure from sea level rise; bridge damage from high winds and scour from runoff and extreme river discharge. Transportation systems also face increasing road closures, transit system shut downs, increasing traffic disruption and emergency evacuations.
The National Climate Assessment notes that transportation agencies can build resilience to these potential impacts through a range of adaptation options. These include use of alternate routes around damaged elements and shifting the public to undamaged modes, new and improved infrastructure designs for future climate conditions, asset management programs, protection of at-risk assets, operational changes, and abandoning/relocating infrastructure assets that would be too expensive to protect.
“As new and rehabilitated transportation systems are developed, climate change impacts should be routinely incorporated into the planning for these systems,” the report noted.
Details on the expected changes in climate conditions and extreme weather, as well as the likely impacts on the highway system, are outlined in a comprehensive research report and practitioner’s guide produced under the National Cooperative Highway Research Program. (see NCHRP Report 750: Strategic Issues Facing Transportation, Volume 2: Climate Change, Extreme Weather Events, and the Highway System: Practitioner’s Guide and Research Report)
The guide outlines “the steps that should be taken if transportation officials want to know what climate stresses the transportation system might face in the future; how vulnerable the system will likely be to these stresses; and what strategies can be considered to avoid, minimize, or mitigate potential consequence.”
It recommends an eight-step diagnostic framework transportation agencies can use to undertake an adaptation assessment, including the following steps:
- Identify key goals and performance measures for the adaptation planning effort.
- Define policies on assets, asset types, or locations that will receive adaptation consideration.
- Identify climate changes and effects on local environmental conditions.
- Identify the vulnerabilities of asset(s) to changing environmental conditions.
- Conduct risk appraisal of asset(s) given vulnerabilities.
- Identify adaptation options for high-risk assets and assess feasibility, cost effectiveness, and defensibility of options.
- Coordinate agency functions for adaptation program implementation (and optionally identify agency/public risk tolerance and set trigger thresholds).
- Conduct site analysis or modify design standards (using engineering judgment), operating strategies, maintenance strategies, construction practices, etc.