Bridge Condition Measures

Structurally Deficient Bridges Report

One of the most prominent measures of bridges is whether or not a bridge is structurally deficient. A structurally deficient (SD) bridge is one for which the deck (driving surface), the superstructure (supports immediately beneath the driving surface), or the substructure (foundation and supporting posts and piers) are rated in condition 4 or less on a scale of 1-10. Structural deficiency does not necessarily imply that a bridge is unsafe. It does, however, mean that a structure is deteriorated to the point of needing repairs immediately to prevent restrictions on the bridge. The ABP Goal is to reduce to 450 the number of SD bridges by 2016.

MassDOT Trend of Structurally Deficient Bridges 1996-Present

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From 1996 to 2006, the number of structurally deficient bridges dropped from 669 to 502 as shown. These improvements reduced the percentage of SD bridges in the state from 15% to 11%. Since 2006, the number of structurally deficient bridges in Massachusetts has remained relatively constant. Recent investments in preservation are beginning to reverse the trend of adding to the SD inventory.

MassDOT Number of SD Bridges Added vs. SD Removed – August 2007 to Present

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This chart shows the number of bridges that became structurally deficient and the number of bridges that were removed from the list of structurally deficient in each month since April 2008. As this chart indicates, through June 2008 bridges became structurally deficient at a faster rate than MassDOT was able to remove bridges from structurally deficient status. This trend is due in large part to unmet maintenance needs on many of Massachusetts’ bridges, especially older bridges. In August 2008, Governor Patrick signed the Accelerated Bridge Program into law to reverse this trend. Recent investments are improving the trend.

DCR Trend of Structurally Deficient Bridges 2005-Present

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From 2005 to present, the number of DCR structurally deficient bridges increased from 21 to 27 out of 106 bridges. The Accelerated Bridge Program will help to reduce the number of DCR SD bridges.

Bridge Health Index Report

MassDOT and DCR also measure bridge condition with Bridge Health Index. Bridge Health Index is the ratio of the current condition of each element to perfect condition expressed as a score from 0 to 100, with a value of zero indicating all of particular bridge’s elements to be in the worst condition. A bridge health index of 85 would indicate that the condition of a system of bridges to be good. Health Index is especially useful to characterize the physical condition of a bridge or set of bridges. Health Index provides MassDOT and DCR bridge engineers with a way of assessing the overall conditions of all bridges, or subsets of bridges, in Massachusetts.

MassDOT Health Index Report

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DCR Health Index Report

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Health Index By Road Category

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The above chart shows a comparison the Health Index of bridges on Interstates, US and State Highways, and local roads. The condition of bridges on the interstates is higher than the condition of US, State, and Local Roads. These better condition of bridges on the interstate system is attributed to the increased focus and funding assistance for Interstate Bridges. Improving Interstate Bridge Health is also a priority of the ABP.