Bridge Condition

How well are we maintaining our bridges?

Bridge Condition

Definition: 
Bridge condition is measured by the share of bridges and overpasses flagged as structurally deficient, weighted by bridge deck area to capture the relative size of the bridge. In short, this measure reflects the integrity of regional bridges and overpasses. Structural deficiency is identified based on the condition of the structure as assessed by engineering professionals (as opposed to just the roadway surface).

Bridges define our region. From the Golden Gate Bridge to the Bay Bridge, they remain iconic symbols of the Bay Area, recognizable to people across the world. But they face great threats from natural hazards, as we witnessed in 1989 when the Loma Prieta earthquake seriously damaged the Bay Bridge. Fundamentally, we want to make sure that they are structurally sound – so not a single life is lost when the next quake hits our region. Investments over the past decade have profoundly enhanced the condition of hundreds of facilities across the region.

Regional Performance
Bay Area bridge conditions have significantly improved over the past decade.

Bay Area bridges and overpasses are in their best shape since 1998, thanks to substantial efforts to improve the seismic and structural safety of these critical facilities. In 2012, the share of bridges flagged as structurally deficient fell by two percentage points – and now stands at just 15 percent.

The region has made dramatic progress in a relatively short time period. In the early 2000s, nearly 20 percent of the region’s bridges were added to the list of deficient facilities, presenting a major infrastructure challenge to regional and state authorities. Over the past decade, seismic retrofit programs on highway bridges as well as upgrades to elevated freeway structures helped to bring about improvements, restoring conditions to levels that had not been seen since the 1990s.

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Historical Trend for Bridge Condition

 
 
Local Focus
Most Bay Area counties have seen significant improvements in bridge and overpass conditions over the last decade, but San Francisco is a major exception.

From 2010 to 2012, the structurally deficient share of bridge deck area in Contra Costa and San Mateo counties fell by two-thirds. Improvements in Alameda, Marin and Solano counties were almost as dramatic, ranging from 47 percent to 62 percent reductions in the share of structurally deficient bridge deck area in those counties. This trend extended to Santa Clara and Sonoma counties, both of which saw their structurally deficient shares of bridge deck area decline by more than a third. But the story was entirely different in San Francisco, which saw its share of structurally deficient bridge deck area rise by more than half, jumping from 26 percent in 2010 to 41 percent in 2012.

Notwithstanding these significant recent improvements, the overall condition of bridges in most counties is still worse in 2012 than it was in 1995. Only Alameda and Contra Costa counties currently have lower shares of structurally deficient bridge deck area than they did in the mid-1990s – and by considerable margins in both cases. The seismic retrofits of those counties’ toll bridges have contributed to their strong performance.

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2012 Bridge Condition

 
 
 
National Context
Despite significant progress, the Bay Area continues to have the greatest share of structurally deficient bridges of any major metro area.

Despite reducing its share of structurally deficient bridge deck area by half since 2005, the Bay Area still finds itself at the bottom of the list of the nation’s top 10 metro areas. The New York City metro area shares the bottom rung for worst bridge condition with the Bay Area, both with structurally deficient bridge deck area shares of 15 percent. While the Bay Area had seen greater gains than any other major metro area, the region still clearly lags its peers in this important measure of infrastructure preservation.

Metro areas in the South generally have the fewest structurally deficient bridges – Dallas, Washington, Atlanta, Miami and Houston all have deficient shares in the low single-digit range. This trend reflects the fact that these regions, due to their recent growth, generally have newer infrastructure and many have fewer geographical features requiring this type of infrastructure. Overall, every metro area except for Los Angeles has seen improvements in bridge condition over the past decade.

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Metro Comparison for Bridge Condition

 
Sources: 

Federal Highway Administration: National Bridge Inventory (1992-2012)

Image: MTC Library (ID# IMG_4901)

Methodology Notes: 

Regional performance was examined by summing all of the bridge deck area flagged as structurally deficient and dividing it by total bridge deck area. Metro comparisons were performed using current MSA boundaries and using the counties included to calculate past performance in those geographies; for the Bay Area, the nine-county region reflects regional performance instead of separate MSAs.