Transportation Infrastructure

The Nation's Highway Bridges Remain at Risk From Earthquakes Gao ID: RCED-92-59 January 23, 1992

The October 1989 Loma Prieta Earthquake devastated the Cypress Viaduct and a section of the Bay Bridge connecting Oakland and San Francisco, killing 43 people. The earthquake also damaged 95 other bridges. In assessing the threat that earthquakes pose to America's bridges, GAO found that bridges in 31 states are at peril from moderate- to high-intensity earthquakes. Yet earthquakes need not be severe to damage bridges. For example, it is estimated that more than one-third of the bridges in Memphis, Tennessee--located near the New Madrid fault--would be damaged by a moderate earthquake; experts project the chance of such an earthquake along the fault at between 40 and 63 percent over the next 15 years. The Federal Highway Administration (FHwA) has encouraged states to identify and retrofit existing bridges along routes vital for national defense, commerce, or emergency evacuation. Despite such efforts, states have done little to identify and correct seismic-related bridge deficiencies. State officials attribute such inaction to limited funding, a lack of technical information available for seismic retrofit work, and a belief that their state has a low risk of earthquake damage. Further, the seismic vulnerability of the nation's bridges is largely unknown. Although FHwA requires states to report annually on the overall structural condition of their bridges, they need not identify bridges subject to earthquakes.

GAO found that: (1) 31 states have bridges that are at risk of damage from moderate- to high-intensity earthquakes; (2) although FHwA has encouraged states to identify and retrofit existing bridges on important defense and evacuation routes and main commuter and commerce routes, states have made limited progress in identifying and correcting seismic-related bridge deficiencies; (3) 8 of the 26 surveyed states at seismic risk stated that they had identified vulnerable bridges and had retrofitted, or were in the process of retrofitting, less than 2 percent of those bridges; (4) states that had made limited attempts to identify and retrofit at-risk bridges cited such reasons for their reluctance to do so as limited funding, a lack of technical retrofit information, and a belief that their states were not at a risk for earthquake damage; (5) although FHwA required states to annually report on their bridges' overall structural condition, it did not require states to identify bridges subject to seismic forces; and (6) because the degree of seismic risk varied among states, FHwA primarily facilitated seismic efforts by providing states with procedural guidance, training, and assistance in state seismic research efforts, but states believed that they needed additional FHwA assistance because they lacked experience and expertise in addressing seismic bridge deficiencies.


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