canes; drought; and rising sea levels, coupled with storm surges and land subsidence. The impacts will vary by mode of transportation and region of the country, but they will be widespread and costly in both human and economic terms and will require significant changes in the planning, design, construction, operation, and maintenance of transportation systems.
Transportation infrastructure was designed for typical weather patterns and environmental conditions, reflecting local climate and incorporating assumptions about a reasonable range of temperatures and precipitation levels. It will be affected most by those climate changes that cause environmental conditions to extend outside the range for which the system was designed.
Finding: Potentially, the greatest impact of climate change for North America’s transportation systems will be flooding of coastal roads, railways, transit systems, and runways because of global rising sea levels, coupled with storm surges and exacerbated in some locations by land subsidence.
Fully 53 percent of the U.S. population now lives in counties with coastal regions, many among the most densely populated in the nation. If development pressures continue in vulnerable coastal areas, and there is every reason to believe they will, the impacts of climate change will be magnified as increasing numbers of people and businesses are placed in harm’s way, and the infrastructure is expanded or new infrastructure is built to accommodate the growth. The Atlantic and Gulf Coasts are particularly vulnerable because they have already experienced high levels of erosion, land subsidence, and loss of wetlands. Their vulnerability to the storm surges and wave action that accompany strong tropical storms was amply demonstrated during the 2005 hurricane season. Sea level rise and coastal flooding also pose risks for the East Coast, as well as the Pacific Northwest and parts of the California coast.
The impacts of climate change will not be limited to coastal areas. For example, watersheds supplying water to the St. Lawrence Seaway and the Great Lakes, as well as the Upper Midwest river system, are likely to experience drier conditions, resulting in lower water levels and reduced capacity to ship agricultural and other bulk commodities, although a longer shipping season could offset some of the adverse economic