National Bridge Inventory
Encyclopedia
The National Bridge Inventory (NBI) is a database, compiled by the Federal Highway Administration
, with information on all bridge
s and tunnel
s in the United States
that have roads passing above or below. This is similar to the grade crossing identifier number database compiled by the Federal Railroad Administration
which identifies all railroad crossings. This bridge information includes the design of the bridge and the dimensions of the usable portion. The data is often used to analyze bridges and judge their conditions. The bridge inventory is developed with the purpose of having a unified database for bridges, including identification information, bridge types and specifications, operational conditions, bridge data including geometric data and functional description, inspection data, etc. Any bridge more than 20 feet (6 meters) long used for vehicular traffic is included.
The bridge inventory is developed for having a unified database for bridges including the identification information, bridge types and specifications, operational conditions, and bridge data including geometric data, functional description, inspection data, etc. Identification information addresses the bridge location uniquely and classifies the type of the routes carried out on and/or under the structure and locates the bridge within the spatial location. Bridge type and specifications classify the type of the bridge. This part provides defined standard categories for classification of the bridges. It also identifies the material of the bridge components, deck and deck surface. Operational conditions provide information about the age of the structure as well as construction year, rehabilitation year, type of services and traffic carried over and/or under the structure number of the lanes over and/or under the bridges, average daily traffic, average daily truck traffic and information regarding to bypass, detours. Furthermore, the bridge inventory contains information regarding to inspection data, ratings assigned by inspectors and appraisal results.
It also classifies bridges as either "structurally deficient" or "functionally obsolete". Neither necessarily implies lack of safety, though that could be a concern as well. "Structurally deficient" means that the condition of the bridge includes a significant defect, which often means that speed or weight limits must be put on the bridge to ensure safety; a structural evaluation of 4 or lower qualifies a bridge as "structurally deficient". The designation can also apply if the approaches flood regularly. "Functionally obsolete" means that the design of a bridge is not suitable for its current use, such as lack of safety shoulders or the inability to handle current traffic volume, speed, size, or weight.
In December 2008, 72,868 bridges in the United States (12.1%) were categorized as "structurally deficient", representing an estimated $48 billion in repairs, and 89,024 (122%) were rated "functionally obsolete", representing an estimated $91 billion in replacement costs.
The Inventory is used for federal funding purposes. A "bridge sufficiency rating" is calculated, based 55% on the structural evaluation, 30% on the obsolescence of its design, and 15% on its importance to the public. As of 2008, a score of 80 or less is required for federal repair funding, and 50 or less for federal replacement funding.
Federal Highway Administration
The Federal Highway Administration is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two "programs," the Federal-aid Highway Program and the Federal Lands Highway Program...
, with information on all bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
s and tunnel
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...
s in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
that have roads passing above or below. This is similar to the grade crossing identifier number database compiled by the Federal Railroad Administration
Federal Railroad Administration
The Federal Railroad Administration is an agency in the United States Department of Transportation. The agency was created by the Department of Transportation Act of 1966...
which identifies all railroad crossings. This bridge information includes the design of the bridge and the dimensions of the usable portion. The data is often used to analyze bridges and judge their conditions. The bridge inventory is developed with the purpose of having a unified database for bridges, including identification information, bridge types and specifications, operational conditions, bridge data including geometric data and functional description, inspection data, etc. Any bridge more than 20 feet (6 meters) long used for vehicular traffic is included.
NBI components
Identification information addresses the bridge location uniquely and classifies the type of the routes carried out on and/or under the structure and locates the bridge within the spatial location. Each bridge is given a number by the highway department of the respective state or the agency that maintains the bridge. The method of assigning numbers differs from one state to the next, but provides a unique number for each bridge in the state.The bridge inventory is developed for having a unified database for bridges including the identification information, bridge types and specifications, operational conditions, and bridge data including geometric data, functional description, inspection data, etc. Identification information addresses the bridge location uniquely and classifies the type of the routes carried out on and/or under the structure and locates the bridge within the spatial location. Bridge type and specifications classify the type of the bridge. This part provides defined standard categories for classification of the bridges. It also identifies the material of the bridge components, deck and deck surface. Operational conditions provide information about the age of the structure as well as construction year, rehabilitation year, type of services and traffic carried over and/or under the structure number of the lanes over and/or under the bridges, average daily traffic, average daily truck traffic and information regarding to bypass, detours. Furthermore, the bridge inventory contains information regarding to inspection data, ratings assigned by inspectors and appraisal results.
Structural evaluation scale
The National Bridge Inventory includes a structural evaluation of deck, superstructure, and substructure, on a 0-9 scale:- 9 Superior to present desirable criteria
- 8 Equal to present desirable criteria
- 7 Better than present minimum criteria
- 6 Equal to present minimum criteria
- 5 Somewhat better than minimum adequacy to tolerate being left in place as is
- 4 Meets minimum tolerable limits to be left in place as is
- 3 Basically intolerable requiring high priority of corrective action
- 2 Basically intolerable requiring high priority of replacement
- 1 This value of rating code not used
- 0 Bridge closed
It also classifies bridges as either "structurally deficient" or "functionally obsolete". Neither necessarily implies lack of safety, though that could be a concern as well. "Structurally deficient" means that the condition of the bridge includes a significant defect, which often means that speed or weight limits must be put on the bridge to ensure safety; a structural evaluation of 4 or lower qualifies a bridge as "structurally deficient". The designation can also apply if the approaches flood regularly. "Functionally obsolete" means that the design of a bridge is not suitable for its current use, such as lack of safety shoulders or the inability to handle current traffic volume, speed, size, or weight.
In December 2008, 72,868 bridges in the United States (12.1%) were categorized as "structurally deficient", representing an estimated $48 billion in repairs, and 89,024 (122%) were rated "functionally obsolete", representing an estimated $91 billion in replacement costs.
Issues and usage
The NBI was subjected to scrutiny and questions, after new actions revealed it might be outdated or inaccurate. Federal officials attempted to order emergency inspections of all steel truss bridges after a major bridge collapse in Minneapolis in 2007. However, it was found that many records within the NBI were inaccurate or out of date.The Inventory is used for federal funding purposes. A "bridge sufficiency rating" is calculated, based 55% on the structural evaluation, 30% on the obsolescence of its design, and 15% on its importance to the public. As of 2008, a score of 80 or less is required for federal repair funding, and 50 or less for federal replacement funding.
External links
- msnbc.com's Bridge Tracker interactive map based on the newest National Bridge Inventory
- msnbc.com investigation: Late inspections of bridges put travelers at risk
- National Bridge Inventory (Data available in ASCII)
- National Bridge Structural Deficiency Data by State/Year Built (Data Available in Excel)
- National Bridge Inventory search (by Alexander Svirsky)
- Navigating the National Bridge Inventory