County profile · official public datasets

Twin Falls County, ID

126 public highway bridges tracked in the FHWA National Bridge Inventory: 12.7% rated Good, 84.1% Fair, 3.2% Poor.

126
Public bridges: 12.7%
Good condition: 3.2%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Twin Falls County pairs a better-than-median Poor-condition share among rated counties in the state with an older average build year than the state inventory.

Top 36%
lowest Poor share in state: 3.2%
Poor-condition share: 126
public highway bridges: 1973
avg year built

Poor is an FHWA condition category from the lowest applicable component rating (4 or below), not a live crossing-safety or closure decision. Rankings cover counties with at least five public highway bridges.

Twin Falls County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Twin Falls County ranks #16 of 44 Idaho counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 3.2%). Twin Falls County, Idaho contains 126 public highway bridges. Roughly 12.7% are rated “Good,” 84.1% “Fair,” and 3.2% “Poor.” Poor means the lowest applicable deck, superstructure, substructure, or culvert rating is 4 or below on the 0–9 NBI scale. It is a condition category, not a live safety or closure decision.

Responsible agencies inspect covered bridges on risk-based intervals under current NBIS rules and submit inventory data to FHWA annually. The list below shows every NBI-tracked bridge in the county. Use the “Sort by” controls to change the ordering, and click any row for its reported inspection date, traffic count, and condition fields.

Source: FHWA National Bridge Inventory. See methodology for full definitions.

Total bridges

126

Public highway bridges in Twin Falls County

Good condition

12.7%

16 of 126 rated 7-9

Fair condition

84.1%

106 of 126 rated 5-6

Poor condition

3.2%

4 of 126 rated 4 or below

In-state Poor-share rank

#16 of 44

Among Idaho counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 126 NBI-tracked bridges by lowest applicable component rating.

Good

12.7% (16)

Fair

84.1% (106)

Poor

3.2% (4)

Twin Falls County's Poor-condition bridges carry 22,400 vehicle crossings a day

That is 8.9% of the county's reported daily bridge traffic on 3.2% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 5,600 crossings a day against 2,192 for a Good-condition one. A Poor rating is a condition category, not a closure or a live safety judgement; it means the lowest applicable component rating is 4 or below.

Computed over the 126 of 126 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

57.9% of Twin Falls County's bridges have passed the 50-year mark

73 of the 126 bridges with a recorded construction year were built in 1974 or earlier. Age alone is not a defect: a well-maintained older bridge can rate Good, and 12.7% of this county's inventory does. Even so, this older cohort is the population from which future Poor ratings are drawn, which is why the age profile below matters alongside the condition split above.

Cutoff derives from the 2024 release year minus a 50-year design life. Source: FHWA National Bridge Inventory, 2024 release.

One structure carries 49.1% of the county's Poor-condition bridge traffic

STC7232;BLUE LAKES over ROCK CREEK, built 1959, carries 11,000 vehicles a day, the most of any Poor-rated structure here. The county's Poor-condition exposure is concentrated rather than evenly spread, so the 4-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 22,400 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1910s

1
1920s

2
1930s

10
1940s

1
1950s

7
1960s

44
1970s

18
1980s

15
1990s

12
2000s

6
2010s

8
2020s

2

What this shows Construction peaked in the 1960s, when 44 of the county's bridges still in the inventory were built, which is 34.9% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year is 1973, 6 years older than the Idaho average of 1979.

How Twin Falls County compares with Idaho's closest counties by inventory size

The 5 Idaho counties nearest Twin Falls County in number of bridges, with their condition splits. Its 3.2% Poor share is the 3rd-lowest of these 6. Its average build year of 1973 against a peer-group mean of 1980 is 7 years older.

Showing the 5 closest of 43 Idaho counties eligible for comparison.

Bridge inventory size and condition shares for Twin Falls County and the 5 Idaho counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Fremont County	137	32.8%	61.3%	5.8%	1983
Custer County	128	34.4%	56.3%	9.4%	1978
Jefferson County	127	17.3%	79.5%	3.1%	1973
Twin Falls County (this page)	126	12.7%	84.1%	3.2%	1973
Bannock County	124	33.1%	62.1%	4.8%	1981
Cassia County	116	15.5%	84.5%	0%	1984

Each share is of that county's own total tracked bridges; peers are the counties with 5 or more bridges whose inventory size is closest to Twin Falls County's. Source: FHWA National Bridge Inventory, 2024 release.

Nationwide counties with similar inventory size or average build year

Two NBI-derived peer sets for Twin Falls County, both outside Idaho so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside ID (126 bridges here).

Bibb County, AL · 126 bridges
Coosa County, AL · 126 bridges
Lawrence County, AR · 126 bridges
Coffee County, GA · 126 bridges

Similar average build year

Nearest mean year-built outside ID (1973 here).

Jefferson County, AL · avg 1973 · 1,068 bridges
Erie County, NY · avg 1973 · 906 bridges
Davidson County, TN · avg 1973 · 832 bridges
Lancaster County, PA · avg 1973 · 801 bridges

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 126 Good 16 Fair 106 Poor 4

Fair-condition bridges (106)

Sort:

Twin Falls County Bridge Snapshot

Condition distribution

Twin Falls County's Poor-condition bridges carry 22,400 vehicle crossings a day

57.9% of Twin Falls County's bridges have passed the 50-year mark

One structure carries 49.1% of the county's Poor-condition bridge traffic

How Twin Falls County compares with Idaho's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

Fair-condition bridges (106)

STC2739;3800 E. RD

1400 EAST ROAD

3100 NORTH ROAD

2800 EAST ROAD

STC2713;3700 N. RD

STC2739;3800 E. RD

SHOESTRING ROAD

2200 EAST RD

CLOVER ROAD

3200 EAST RD

2000 EAST ROAD

1050 EAST ROAD

3200 NORTH RD

3300 NORTH ROAD

3500 EAST ROAD

2300 EAST ROAD

3800 NORTH RD

2300 EAST RD

BASIN CUTOFF ROAD

4000 NORTH ROAD

3600 EAST RD

STC2705;1400 E. RD

1600 EAST RD

STC2739;3800 E. RD

3300 EAST RD

STC2713;CROSS CNTY

STC2721;2200 E. RD

STC2729;3400 N. RD

1900 EAST ROAD

2700 EAST ROAD

2500 NORTH ROAD

3800 NORTH ROAD

3100 EAST ROAD

1500 EAST ROAD

2100 EAST RD

3400 NORTH RD

1500 EAST ROAD

2200 NORTH ROAD

3500 EAST ROAD

1900 EAST ROAD

2800 EAST RD

N 2700 E

2500 EAST ROAD

N 1700 E

3200 EAST RD

3950 NORTH RD

2500 EAST ROAD

2300 EAST RD

3600 NORTH RD

RIVER ROAD

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