What does the term “structurally deficient” mean? That’s exactly the question Senator Inhofe asked  Secretary Mary E. Peters, Secretary U.S. Department of Transportation, to address during this week’s Senate Environment and Public Works hearing examining the condition of our nation’s bridges. In the aftermath of catastrophic failure of the I-35 bridge in Minnesota , the term has caused significant confusion.  

Secretary Peters explains in her prepared remarks before the EPW Committee that the term “structurally deficient” is a technical engineering term:

“The term ‘structurally deficient’ is a technical engineering term used to classify bridges according to serviceability, safety, and essentiality for public use. The fact that a bridge is classified as ‘structurally deficient’ does not mean that it is unsafe for use by the public. Since 1995 the percentage of travel taking place on roads that are considered “good” has increased from 39.8% to 44.2%.Overall, approximately 85% of travel takes place on pavement that is considered ‘acceptable.’”

Calvin L. Scovel, the Inspector General U.S. Department of Transportation, also addresses the question of what “structural deficient” in his prepared remarks before the Committee:

“The term ‘structurally deficient’ refers to bridges that have major deterioration, cracks, or other deficiencies in their structural components, including decks, girders, or foundations. Regular inspections that check for corrosion, decay, and other signs of deterioration are important tools for ensuring that bridges are safe. In some cases, structurally deficient bridges require repair of structural components, or even closure. But most bridges classified as structurally deficient can continue to serve traffic safely if they are properly inspected, the bridges’ maximum load ratings are properly calculated, and, when necessary, the proper maximum weight limits are posted.”

FACT: Of the 600,000 Bridges in the United States , only 2% are owned by the Federal Government, the rest are owned by the States (47%) and local government (51%).   States are ultimately responsible for inspection of all public highway bridges within the state, except for the small number owned by the Federal government and Indian tribes; the bridge owners are responsible for actually completing the inspection.  Most bridges, including all of those that are longer than 20ft and on the Federal-Aid system, are inspected at least every 2 years.  The National Bridge Inspection Program also includes specific qualifications and a training program for bridge inspectors.  Information collected from each inspection is transmitted to the Federal Highway Administration (FHWA) and entered into the NBI database.  This information is then used to assure bridge safety and to determine which bridges are eligible for funding. Each bridge in the National Bridge Inventory has both a sufficiency rating and a condition rating. 

Sufficiency Ratings (from 0 – 100 with 0 being the worst) are used to illustrate the bridge’s overall capability.  A bridge’s structural deficiency makes up 55% of the sufficiency rating.  The sufficiency rating is based:  

*55% on structural condition

*30% on ability to meet current traffic conditions

*15% on how essential it is for public use

Bridges with a sufficiency rating of less than 50 are eligible for replacement or rehabilitation and those with a sufficiency rating of less than 80 are eligible for rehabilitation.  Highway Bridge Program funds are available for both activities.

Condition Ratings (from 0 – 9 with 0 being the worst) are used to determine whether a bridge is functionally obsolete and/or structurally deficient.  Condition ratings are based on the condition of the bridge deck, superstructure, and piers.  A bridge with a condition rating of 1 – 4 is considered functionally obsolete and/or structurally deficient. 

There are two types of deficient bridges:

Structurally Deficient:  a bridge which has deteriorated conditions of significant bridge elements and reduced load carrying capacity, or the waterway opening beneath the bridge is insufficient and causing significant traffic interruptions.  A structurally deficient bridge is often weight limited, requires immediate rehabilitation to remain open, or is closed.

Functionally Obsolete:  a bridge that has a deck geometry, load carrying capacity, clearance or approach roadway alignment that does not meet current design standards.  Functional obsolescence is the result of changing traffic demands and design standards rather than a degradation of the bridge itself.

Rural bridges are more often structurally deficient, while urban bridges are usually functionally obsolete due to increased traffic.  About 28% of all bridges are deficient.  If a bridge is both structurally deficient and functionally obsolete, it is classified as structurally deficient.  Approximately 72,000 bridges are considered structurally deficient and 81,000 are considered functionally obsolete. Of those bridges that are classified as structurally deficient, approximately 6,000 are on the National Highway System.

Putting the Bridge Crisis in Perspective

Although we must take very seriously the collapse of the I35 bridge in Minnesota by taking a much closer look at how bridges are funded and maintained, when we examine our nation’s infrastructure in its entirety, we will find that it is not just bridges but all aspects of our national highway system that needs attention.  The investment needs for aging bridges are staggering, but we cannot let this overshadow the overwhelming needs on all aspects our nation’s highways.