National Bridge Inventory: Idaho



  • Of the 4,522 bridges in the state, 286, or 6.3 percent, are classified as structurally deficient. This means one of the key elements is in poor or worse condition.
  • This is down from 360 bridges classified as structurally deficient in 2016.
  • The deck area of structurally deficient bridges accounts for 5.0 percent of total deck area on all structures.
  • 17 of the structurally deficient bridges are on the Interstate Highway System. A total of 90.2 percent of the structurally deficient bridges are not on the National Highway System, which includes the Interstate and other key roads linking major airports, ports, rail and truck terminals.
  • 428 bridges are posted for load, which may restrict the size and weight of vehicles crossing the structure.
  • The state has identified needed repairs on 1,543 bridges at an estimated cost of $1.6 billion.
  • This compares to 1,619 bridges that needed work in 2016.

County Year Built Daily Crossings Type of Bridge Location
Bannock 1962 18,500 Urban Interstate I 15 SBL over I 86 EB Ramp
Bannock 1962 18,500 Urban Interstate I 15 SBL over I 86 WB Ramp
Madison 1971 17,000 Urban other principal arterial SH 33 over S.Fk.Teton River
Bingham 1965 14,000 Urban other principal arterial US 26 EBL & WBL over Snake River;W.Blackfoot
Ada 1963 13,500 Rural Interstate I 84 EBL over Kuna Rd;Blacks Creek Ic
Ada 1963 13,500 Rural Interstate I 84 WBL over Kuna Rd;Blacks Creek Ic
Bingham 1961 13,000 Rural Interstate I 15 NBL over I15B;UPRR;S.Blackfoot Ic
Bingham 1961 13,000 Rural Interstate I 15 SBL over I15B;UPRR;S.Blackfoot Ic
Kootenai 1960 12,000 Urban Interstate I 90 WBL over STC 7405;Penn.Ave.Gs
Bannock 1967 11,500 Urban other principal arterial STP 7151;Benton St over First Ave;UPRR;Benton Op
Elmore 1974 8,750 Rural Interstate I 84 EBL over Snake R;E.Snake River Br
Elmore 1974 8,750 Rural Interstate I 84 WBL over Snake R;E.Snake River Br
Fremont 1973 8,700 Rural arterial US 20 WBL & EBL over S.Fk.Fall River Canal
Bannock 1962 8,500 Rural Interstate I 15 NBL over I 15B;W.Inkom Ic
Bannock 1962 8,500 Rural Interstate I 15 NBL over Main Street Gs
Bannock 1962 8,500 Rural Interstate I 15 SBL over Main Street Gs
Shoshone 1972 7,400 Rural Interstate I 90 EBL & WBL over RR Roadbed/No Tracks
Owyhee 1955 7,000 Rural arterial SH 55 over Snake River(Marsing Br)
Bingham 1936 6,600 Urban other principal arterial I 15B ;US 91 over Blackfoot River
Shoshone 1969 6,500 Rural Interstate I 90 EBL over Elizabeth Park Road Gs
Shoshone 1969 6,500 Rural Interstate I 90 WBL over Elizabeth Park Road Gs
Boise 1934 6,500 Rural arterial SH 55 over Payette River
Bingham 1936 6,100 Urban minor arterial SMA 7611;W. Bridge over Snake River
Shoshone 1963 5,000 Rural Interstate I 90 WBL over Golconda Access Road Ic
Kootenai 1936 4,500 Rural arterial SH 53 over Union Pacific Railroad
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 273 214,503 2,205,040 14 16,382 123,100
Rural arterial 337 289,011 1,839,850 9 9,925 40,900
Rural minor arterial 240 127,079 521,620 3 748 8,300
Rural major collector 729 259,000 768,894 35 15,673 29,640
Rural minor collector 276 54,980 82,297 17 3,601 4,132
Rural local road 1,996 275,797 297,656 186 23,246 18,881
Urban Interstate 114 115,180 2,719,550 3 2,160 49,000
Urban freeway/expressway 0 0 0 0 0 0
Urban other principal arterial 187 251,942 2,984,900 4 10,724 49,100
Urban minor arterial 158 116,870 1,383,190 3 3,630 11,700
Urban collector 108 34,563 331,250 7 2,219 14,210
Urban local road 104 36,092 109,193 5 903 2,950
Total 4,522 1,775,017 13,243,440 286 89,212 351,913
Type of Work Number of Bridges Cost to Repair
(in millions)
Daily Crossings Area of Bridges
(sq. meters)
Bridge replacement 1,403 $1,432 3,307,397 565,407
Widening & rehabilitation 40 $34 178,298 20,118
Rehabilitation 74 $68 113,302 39,015
Deck rehabilitation/replacement 6 $6 2,930 3,436
Other structural work 20 $27 90,280 15,218
Total 1,543 $1,566 3,692,207 643,194

About the data:

Data is from the Federal Highway Administration (FHWA) National Bridge Inventory (NBI), downloaded on March 11, 2021. Note that specific conditions on bridges may have changed as a result of recent work or updated inspections. Cost estimates were downloaded by ARTBA on March 11, 2021.

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 2019 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.

28
Compared to 29 in 2019

in the nation in % of structurally deficient bridges

1. West Virginia 21.2%
27. Wisconsin 6.9%
28. Idaho 6.3%
29. California 6.0%

37
Compared to 37 in 2019

in the nation in # of structurally deficient bridges

1. Iowa 4,571
36. Maine 315
37. Idaho 286
38. Puerto Rico 282

26
Compared to 28 in 2019

in the nation in % of structurally deficient bridge deck area

1. Rhode Island 21.0%
25. Colorado 5.0%
26. Idaho 5.0%
27. Kentucky 5.0%
Full State Ranking

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  • Source: Data is from the Federal Highway Administration (FHWA) National Bridge Inventory (NBI), downloaded on March 11, 2021. Note that specific conditions on bridges may have changed as a result of recent work or updated inspections.

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