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
(sq. meters)
Daily Crossings on All Bridges Number of Structurally Deficient Bridges Area of Structurally Deficient Bridges
(sq. meters)
Daily Crossings on Structurally Deficient Bridges
Rural Interstate 276 214,694 1,986,440 8 3,344 58,250
Rural arterial 330 286,883 1,646,900 6 7,464 26,200
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 Interstate 114 115,125 2,441,050 3 2,161 41,250
Urban freeway/expressway 0 0 0 0 0 0
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 collector 107 34,304 324,310 9 2,431 18,050
Urban local road 103 35,952 104,173 6 941 5,560
Total 4,482 1,756,871 12,156,624 315 84,873 294,116
Type of Work Number of Bridges Cost to Repair
(in millions)
Daily Crossings Area of Bridges
(sq. meters)
Bridge replacement 1,431 $1,070 3,174,311 566,846
Widening & rehabilitation 58 $10 236,218 28,331
Rehabilitation 94 $30 105,902 41,169
Deck rehabilitation/replacement 5 $1 2,410 3,389
Other structural work 13 $6 56,495 6,270
Total 1,601 $1,117 3,575,336 646,006

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.

29
from 27 in 2017

in the nation in % of structurally deficient bridges

1. Rhode Island 23.1%
28. California 7%
29. Idaho 7.0%
30. Hawaii 6.9%

37
from 35 in 2017

in the nation in # of structurally deficient bridges

1. Iowa 4,675
36. Maine 325
37. Idaho 315
38. Connecticut 308
Full State Ranking

  • Source: Bridge data is from the 2018 National Bridge Inventory ASCII files, released by the Federal Highway Administration on March 14, 2019. Note that specific conditions on bridges may have changed as a result of recent work. ARTBA is a non-partisan federation whose primary goal is to aggressively grow and protect transportation infrastructure investment to meet the public and business demand for safe and efficient travel.
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