National Bridge Inventory: Idaho



  • The state has identified needed repairs on 1,511 bridges.
  • This compares to 1,561 bridges that needed work in 2021.
  • Over the life of the IIJA, Idaho will receive a total of $225.0 million in bridge formula funds, which will help make needed repairs.
  • Idaho currently has access to $180.0 million of that total, and has committed $165.4 million towards 103 projects as of June 2025.
  • Of the 4,646 bridges in the state, 250, or 5.4 percent, are classified as structurally deficient. This means one of the key elements is in poor or worse condition.
  • This is up from 238 bridges classified as structurally deficient in 2021.
  • The deck area of structurally deficient bridges accounts for 3.8 percent of total deck area on all structures.

Top Most Traveled Structurally Deficient Bridges in Idaho

County Year Built Daily Crossings Type of Bridge Location
Kootenai 1971 31,250 Urban Interstate I 90 WBL over Pedestrian/Bike Path
Bonneville 1994 27,500 Urban other principal arterial S 25 E; S Hitt Rd over Sand Creek
Canyon 1956 19,500 Urban other principal arterial Nhs 7773;10th Ave over City St;UPRR;Caldwell Op
Bonneville 1984 18,000 Urban other principal arterial Stp7046;Lincoln Rd over Idaho Canal
Bingham 1961 13,750 Rural Interstate I 15 SBL over I15B;UPRR;S.Blackfoot Ic
Bingham 1961 13,750 Rural Interstate I 15 NBL over I15B;UPRR;S.Blackfoot Ic
Twin Falls 1959 11,500 Urban collector Stc7232;Blue Lakes over Rock Creek
Bannock 1962 7,750 Rural Interstate I 15 SBL over Main Street Gs
Bannock 1962 7,750 Rural Interstate I 15 NBL over I 15B;W.Inkom Ic
Bannock 1962 7,750 Rural Interstate I 15 NBL over Main Street Gs
Lemhi 1926 7,300 Rural arterial US 93 over Salmon River;Salmon Br.
Ada 1964 7,000 Urban minor arterial SMA 7643;Healy Rd over New York Canal
Bingham 1936 7,000 Urban other principal arterial I 15B ;US 91 over Blackfoot River
Bingham 1936 6,900 Urban minor arterial SMA 7611;W. Bridge over Snake River
Ada 1954 6,700 Urban minor arterial SMA 7643;Eckert Rd over Ridenbaugh Canal
Ada 1954 6,700 Urban minor arterial SMA 7643;Eckert Rd over Boise River(Barber Br)
Latah 1992 6,400 Urban minor arterial SMA 7674;Mtn View over Paradise Creek
Twin Falls 1973 6,000 Urban minor arterial Stc2714;37 North over Rock Creek
Teton 1975 5,600 Rural minor arterial SH 33 over Spring Creek
Canyon 1966 5,400 Urban other principal arterial Blaine St over Old Indian Creek Channel
Payette 1953 5,100 Urban minor arterial SH 52 over Snake River;Payette Br.
Bingham 1951 4,600 Rural minor arterial US 91 over Blackfoot Canal
Valley 1933 4,100 Rural arterial SH 55 over UPRR;N.Fk.Payette River
Kootenai 2012 3,800 Rural major collector Bunco Road over Bunco Rd; US 95 Ic
Bingham 1923 3,800 Rural arterial US 91 over Gibson Lateral Canal

Bridge Inventory: Idaho

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 277 221,097 2,445,790 7 4,641 52,520
Rural arterial 343 300,460 2,148,950 4 4,195 18,300
Rural minor arterial 252 144,108 703,250 7 3,062 18,140
Rural major collector 767 270,918 1,025,646 31 17,924 22,000
Rural minor collector 232 49,373 92,606 18 4,086 6,066
Rural local road 2,120 302,173 379,667 166 21,451 19,382
Urban Interstate 118 129,318 3,207,600 1 491 31,250
Urban freeway/expressway 0 0 0 0 0 0
Urban other principal arterial 189 257,774 3,392,950 5 5,501 77,400
Urban minor arterial 145 101,289 1,499,080 8 6,232 46,800
Urban collector 89 32,902 335,660 3 1,781 16,400
Urban local road 114 36,831 157,928 0 0 0
Total 4,646 1,846,243 15,389,127 250 69,365 308,258

Proposed Bridge Work

Type of Work Number of Bridges Cost to Repair
(in millions)
Daily Crossings Area of Bridges
(sq. meters)
Bridge replacement 1,363 $2,081 3,587,129 559,927
Widening & rehabilitation 24 $36 68,485 14,212
Rehabilitation 100 $113 124,232 44,758
Deck rehabilitation/replacement 6 $7 2,670 2,588
Other structural work 18 $27 99,971 10,848
Total 1,511 $2,264 3,882,487 632,333

About the data:

Data and cost estimates are from the Federal Highway Administration (FHWA) National Bridge Inventory (NBI), downloaded on August 20, 2024. 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 2023 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 repair cost estimate is supplied by the bridge owner or the bridge is classified as structurally deficient. Please note that for a few states, the number of bridges needing to be repaired can vary significantly from year to year, and reflects the data entered by the state.

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
Compared to 33 in 2024

in the nation in % of structurally deficient bridges

1. Iowa 19.0%
28. Washington 6.0%
29. Idaho 5.0%
30. Arkansas 5.0%

38
Compared to 39 in 2024

in the nation in # of structurally deficient bridges

1. Iowa 4,424
37. Georgia 263
38. Idaho 250
39. Maryland 240

34
Compared to 38 in 2024

in the nation in % of structurally deficient bridge deck area

1. West Virginia 13.0%
33. Ohio 4.0%
34. Idaho 4.0%
35. Colorado 4.0%
Full State Ranking

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  • Source: Data is from the Federal Highway Administration (FHWA) National Bridge Inventory (NBI), downloaded on August 20, 2024. Note that specific conditions on bridges may have changed as a result of recent work or updated inspections.

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