Bridge Condition | Vital Signs

How well are the region’s bridges maintained?

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

14%

of bridge and overpass deck area in Napa is structurally deficient, the worst of any county

The Bay Area ranks #1 for the largest reduction in the share of structurally deficient bridges of any major metro area

2004

was the region’s worst year for bridge condition, with an improving trend ever since

of Bay Area bridges and overpasses are considered structurally deficient, the best performance in the past 24 years

Regional Performance

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

Bay Area bridges and overpasses are in their best shape since 1992 – the earliest year on record – thanks to substantial efforts to improve the seismic and structural safety of these critical facilities. Poor bridge conditions hit a peak in 2004 when nearly one-third of the Bay Area’s bridges were identified as structurally deficient. Over the past 12 years, seismic retrofit programs on highway bridges as well as upgrades to elevated freeway structures helped the region reverse that trajectory. As a result, the share of bridges flagged as deficient fell by a remarkable 25 percentage points – and stood at just 7 percent as of 2016.

Historical Trend for Bridge Condition

Local Focus

While most Bay Area counties have seen improved bridge and overpass conditions over the last decade, in recent years San Francisco has experienced the greatest progress.

The share of structurally deficient bridges and overpasses in San Francisco County in 2016 are at an all-time recorded low. Numerous structural repairs were made between 2012 and 2014 and the share of structurally deficient deck area fell by nearly 70 percent in that two-year period. Sonoma, Solano, Contra Costa and Alameda counties have also seen improvements over the past decade, though the rate of repair has slowed considerably in the last four years. In Alameda and Contra Costa counties, the seismic retrofits of those counties’ toll bridges have contributed to their strong performance.

2016 Bridge Condition

All Bridges Deficient Bridges

National Context

As a result of significant investments, the Bay Area no longer has the greatest share of structurally deficient bridges of any major metro area.

Overall, every metro area except for Miami has seen improvements in bridge condition since 2000. Having reduced its share of structurally deficient bridge deck area by 25 percentage points since 2005, the Bay Area finds itself in the middle of the pack of the nation’s top 10 metro areas for bridge condition. New York now claims the bottom rung for worst bridge condition, with structurally deficient bridge deck area shares of 11 percent. While the Bay Area had seen by far the largest gains, Los Angeles has also made notable progress over the last four years.

Metro areas in the South generally have the fewest structurally deficient bridges – Houston, Miami, Atlanta and Dallas all have deficient shares below 3 percent. 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.

Metro Comparison for Bridge Condition

Sources:

Federal Highway Administration: National Bridge Inventory (1992-2016)

http://www.fhwa.dot.gov/bridge/nbi.cfm

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.