National Bridge Inventory: Idaho
- Of the 4,482 bridges in the state, 315, or 7.0 percent, are classified as structurally deficient. This means one of the key elements is in poor or worse condition.
- This is down from 364 bridges classified as structurally deficient in 2014.
- 11 of the structurally deficient bridges are on the Interstate Highway System.
- 417 bridges are posted for load, which may restrict the size and weight of vehicles crossing the structure.
- The state has identified needed repairs on 1,601 bridges at an estimated cost of $1.1 billion.
- This compares to 1,581 bridges that needed work in 2014.
|County||Year Built||Daily Crossings||Type of Bridge||Location|
|Madison||1971||16,000||Urban other principal arterial||SH 33 over S.Fk.Teton River|
|Bannock||1962||15,000||Urban Interstate||I 15 SBL over I 86 WB Ramp|
|Bannock||1962||15,000||Urban Interstate||I 15 SBL over I 86 EB Ramp|
|Bingham||1965||14,000||Urban other principal arterial||US 26 EBL & WBL over Snake River;W.Blackfoot|
|Bannock||1967||13,000||Urban other principal arterial||STP 7151;Benton St over First Ave;UPRR;Benton Op|
|Canyon||1956||13,000||Urban other principal arterial||STP 7773;10th Ave over Indian Creek|
|Ada||1963||11,500||Rural Interstate||I 84 WBL over Kuna Rd;Blacks Creek Ic|
|Ada||1963||11,500||Rural Interstate||I 84 EBL over Kuna Rd;Blacks Creek Ic|
|Kootenai||1960||11,250||Urban Interstate||I 90 WBL over STC 7405;Penn.Ave.Gs|
|Fremont||1973||7,600||Rural arterial||US 20 WBL & EBL over S.Fk.Fall River Canal|
|Bannock||1962||7,450||Rural Interstate||I 15 NBL over I 15B;W.Inkom Ic|
|Bannock||1962||7,450||Rural Interstate||I 15 SBL over Main Street Gs|
|Bannock||1962||7,450||Rural Interstate||I 15 NBL over Main Street Gs|
|Bingham||1936||6,200||Urban other principal arterial||I 15B ;US 91 over Blackfoot River|
|Shoshone||1969||6,000||Rural Interstate||I 90 EBL over Elizabeth Park Road Gs|
|Owyhee||1955||6,000||Rural arterial||SH 55 over Snake River(Marsing Br)|
|Bingham||1936||6,000||Urban minor arterial||SMA 7611;W. Bridge over Snake River|
|Shoshone||1969||6,000||Rural Interstate||I 90 WBL over Elizabeth Park Road Gs|
|Shoshone||1967||5,700||Rural major collector||Stc 5764 Main St over Pine Creek|
|Boise||1934||5,600||Rural arterial||SH 55 over Payette River|
|Bonner||1966||4,700||Rural minor arterial||SH 41 over Burlington Northern RR|
|Bannock||1950||4,100||Urban collector||Stc 7221;Carson St over Portneuf River|
|Gem||1940||3,500||Urban collector||Main Street over Farmers Coop Canal|
|Bonneville||1962||3,400||Urban collector||Stc 7486;12th St. over Idaho Canal|
|Bannock||1969||3,300||Urban collector||Benton Street over Portneuf River|
|Type of Bridge||Number of Bridges||Area of All Bridges
|Daily Crossings on All Bridges||Number of Structurally Deficient Bridges||Area of Structurally Deficient Bridges
|Daily Crossings on Structurally Deficient Bridges|
|Rural minor arterial||239||124,240||490,250||8||3,955||15,230|
|Rural major collector||721||253,421||719,454||41||19,394||35,780|
|Rural minor collector||271||54,030||69,449||19||4,579||3,537|
|Rural local road||1,978||272,810||280,678||208||26,705||20,359|
|Urban other principal arterial||188||251,345||2,796,800||5||10,991||62,200|
|Urban minor arterial||155||114,067||1,297,120||2||2,907||7,700|
|Urban local road||103||35,952||104,173||6||941||5,560|
|Type of Work||Number of Bridges||Cost to Repair
|Daily Crossings||Area of Bridges
|Widening & rehabilitation||58||$10||236,218||28,331|
|Other structural work||13||$6||56,495||6,270|
About the data:
Data from the Federal Highway Administration (FHWA) National Bridge Inventory (NBI), released March 15, 2019. Note that specific conditions on bridges may have changed as a result of recent work or updated inspections.
Effective January 1, 2018, FHWA changed the definition of structurally deficient as part of the final rule on highway and bridge performance measures, published May 20, 2017 pursuant to the 2012 federal aid highway bill Moving Ahead for Progress in the 21st Century Act (MAP-21). Two measures that were previously used to classify bridges as structurally deficient are no longer used. This includes bridges where the overall structural evaluation was rated in poor or worse condition, or where the adequacy of waterway openings was insufficient.
The new definition limits the classification to bridges where one of the key structural elements—the deck, superstructure, substructure or culverts, are rated in poor or worse condition. During inspection, the conditions of a variety of bridge elements are rated on a scale of 0 (failed condition) to 9 (excellent condition). A rating of 4 is considered “poor” condition.
Cost estimates have been derived by ARTBA, based on 2017 average bridge replacement costs for structures on and off the National Highway System, published by FHWA. Bridge rehabilitation costs are estimated to be 68 percent of replacement costs. A bridge is considered to need repair if the structure has identified repairs as part of the NBI, a cost estimate is supplied by the bridge owner or the bridge is classified as structurally deficient.
Bridges are classified by FHWA into types based on the functional classification of the roadway on the bridge. Interstates comprise routes officially designated by the Secretary of Transportation. Other principal arterials serve major centers of urban areas or provide mobility through rural areas. Freeways and expressways have directional lanes generally separated by a physical barrier, and access/egress points generally limited to on- and off-ramps. Minor arterials serve smaller areas and are used for trips of moderate length. Collectors funnel traffic from local roads to the arterial network; major collectors have higher speed limits and traffic volumes and are longer in length and spaced at greater intervals, while minor collectors are shorter and provide service to smaller communities. Local roads do not carry through traffic and are intended for short distance travel.