I-Jobs-Iowa’s Infrastructure Investment Initiative

Bridge Safety Fund


Senate File 376 appropriated $50 million to the Iowa DOT for deposit in the Bridge Safety Fund. The Act also created the Bridge Safety Fund (Iowa Code section 313.68) in the Iowa DOT under the authority of the Iowa Transportation Commission. Monies in the fund shall be used for infrastructure projects relating to functionally obsolete and structurally deficient bridges on the Primary Road System.

The Iowa DOT is required to adopt rules pursuant to Iowa Code Chapter 17A to administer this program. Once adopted, the rules will be made available on this Web site.

National Bridge Inspection Standards (NBIS)

I-74 BridgeThe NBIS sets the national standards for the proper safety inspection and evaluation of all highway bridges in accordance federal law (codified in 23 U.S.C. 151). The NBIS regulations apply to all publicly owned highway bridges longer than 20 feet located on public roads. Railroad and pedestrian structures that do not carry highways are not covered by the NBIS regulations.

In accordance with the NBIS regulations, bridges shall be inspected every two years, or more often, if deemed necessary. While the State of Iowa is ultimately responsible for the inspection of all public highway bridges within the state, except for those that are federally or tribally owned, the state delegates bridge inspection policies and procedures, quality assurance and quality control, preparation and maintenance of a bridge inventory, bridge inspections, reports, load ratings, and other requirements of these standards to local jurisdictions.

For more information about NBIS, visit the Federal Highway Administration's (FHWA) Web site.

National Bridge Inventory (NBI)

The NBI is a collection of information (database) covering just under 600,000 of the nation's bridges located on public roads, including interstate highways, U.S. highways, state and county roads, as well as publicly-accessible bridges on federal lands. It presents a state-by-state summary analysis of the number, location and general condition of highway bridges within each state.

I-74 BridgeCollection of NBI data is authorized by statute, 23 U.S.C. 151 (National Bridge Inspection Program), and implemented by regulation, 23 CFR 650.301 et seq. In accordance with these authorities, the FHWA established NBIS for the safety inspection and evaluation of highway bridges; and each state is required to conduct periodic inspections of all bridges subject to the NBIS, prepare and maintain a current inventory of these structures, and report the data to the FHWA using the procedures and format outlined in the Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges.

After evaluation of the inspection data, the FHWA provides states with a list of bridges that are eligible for replacement or rehabilitation. The FHWA uses the data to submit a required biannual report to Congress on the status of the nation's bridges, publish an Annual Materials Report on New Bridge Construction and Bridge Rehabilitation in the Federal Register, and apportion funds for the Highway Bridge Program.

Use of the NBI data also enables FHWA to satisfy its requirements under 23 U.S.C. 144, which mandate the inventory, classification, cost estimates for replacement or rehabilitation, and assignment of replacement or rehabilitation priorities for all highway bridges on all public roads.

Replacement or major rehabilitation of structurally deficient and functionally obsolete bridges

Highway Bridge ProgramAny bridge maintained by the Iowa Department of Transportation that has a sufficiency rating below 50, is considered eligible for replacement. Bridges with a sufficiency rating above 50 needing to rehabilitation may be eligible for replacement if a life-cycle analysis indicates it is more cost-effective to replace the bridge rather than rehabilitate it.


The terms "structurally deficient," "functionally obsolete" and "sufficiency rating" are defined within the NBIS and used to identify bridges eligible for the federal Highway Bridge Program. The terms were also used in the I-JOBS legislation. The meanings of these terms in the Iowa law are assumed to be the same as the federal definitions.

Structurally deficient: Refers to bridges needing significant maintenance attention, rehabilitation or replacement. A structurally deficient bridge may be posted for a lower weight. A bridge is classified as structurally deficient when the:
Highway Bridge Program
  • Deck, superstructure, substructure and/or culver rated 4 or less (poor or worse condition).
  • Structural condition or waterway adequacy rated 2 or less.
Functionally obsolete: Refers to bridges with deck geometry (e.g., lane width, shoulder widths), load carrying capacity, vertical clearance or approach roadway alignment that no longer meet the criteria for the system of which the bridge is a part. A bridge is classified as functionally obsolete when the:
  • Deck geometry rated 3 or less (e.g., bridge is too narrow)
  • Underclearance rated 3 or less (e.g., a bridge over an interstate route with a clearance of less than 15 feet)
  • Approach roadway alignment rated 3 or less (e.g., crossing the bridge requires a significant speed reduction due to horizontal or vertical curvature of the roadway at the bridge)
Bridges that qualify as both structurally deficient and functionally obsolete are categorized as structurally deficient. Bridges built or reconstructed within the last 10 years are not counted by the Federal Highway Administration as structurally deficient or functionally obsolete.

Bridge sufficiency rating: A bridge's sufficiency rating is calculated on scale of 1 to 100 for the NBI, with 100 being the highest, and it compares the existing bridge to a new bridge designed to current engineering standards.

The sufficiency rating is determined following completion of the bridge inspection process, which involves an examination of the structural condition of the bridge, traffic volumes, number of lanes, road widths, clearances, and importance for national security and public use, to name just a few.

The sufficiency rating is calculated per a formula defined in Federal Highway Administration's Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges. This rating is indicative of a bridge's sufficiency to remain in service. The formula places 55 percent value on the structural condition of the bridge, 30 percent on its serviceability and obsolescence, 15 percent on its essentiality to public use, and up to 13 percent for special reductions.

The bridge's sufficiency rating provides an overall measure of the bridge's condition and is used to determine eligibility for federal funds under the Highway Bridge Program.

Bridge life and public safety

Throughout their life, bridges experience a natural aging process. And, each bridge is unique in the way it ages, and adapts to stresses, its environment and other conditions.

The life of a bridge also varies greatly and is determined by its use and materials. While many bridges in Iowa were constructed decades earlier, the majority continues to serve the needs of the traveling public. Until a bridge reaches the end of its useful life, it may continue to serve Iowans for many years, when adequately maintained and preserved.

The fact that a bridge is rated as "structurally deficient" or "functionally obsolete", or has a low sufficiency rating, does not imply in any way that it is unsafe. Any bridge found to be unsafe to carry traffic will or is already closed.

Bridges incapable of carrying today's maximum load weights may be posted with a weight limit as a means of extending their useful lives. Structurally deficient bridges typically require significant maintenance and repair to remain in service, and will eventually require rehabilitation or replacement to address their deficiencies.

Iowa's Primary Highway System bridge ratings

There are more than 24,000 bridges and structures in Iowa. The Iowa DOT is responsible for 4,092 that are part of the state’s Primary Highway System, which includes the interstate, U.S. and "Iowa"/state highways.

The most recent data summarizing the bridge and structure ratings for the Primary Highway System is dated April 1, 2009. Among the total structures, 232 are classified as structurally deficient and 311 functionally obsolete. The majority (3,549 or 87 percent) of bridges on the Primary Highway System do not fall into either of these categories.

Project candidate list

Project candidate map

Iowa's Primary Highway System bridges

Information about Iowa's Primary Highway System bridges is available online. Data for each bridge includes: the year the bridge was built; year the bridge was reconstructed, if it has undergone major work;, average annual daily traffic count (AADT); highway carried; feature crossed (waterway, highway, railroad, drainage ditch, etc.); sufficiency rating; and whether the bridge is classified as structurally deficient and/or functionally obsolete. Visit Bridges in Iowa to access the bridge information, which is available using a Google Earth™ mapping tool or in PDF format. 

Commission action: approved projects

Approved projects map

Maintenance of Effort

The purpose of the Bridge Safety Fund is to provide a financial boost toward reducing the number of structurally deficient or functionally obsolete bridges on the state’s primary highway system. As such, the Iowa DOT has established a maintenance of effort condition whereby the department will maintain a state/federal (non-I-JOBS funding) fiscal effort equal to $50 million in its bridge preservation and replacement program, spread out over both the I-JOBS implementation period and life of the current FY 2010–2014 Five Year Transportation Improvement Program.  This means that a $50 million increased level of funding will be dedicated to reducing the number of structurally deficient and functionally obsolete bridges on the state system beyond what is already programmed for this effort. The FY2010-2014 Iowa Transportation Improvement Program, approved June 9, 2009, specifically allocates $36 million annually for non-interstate, and approximately $20 million annually for interstate bridge preservation and replacement projects.