County profile · official public datasets

Jefferson County, ID

127 public highway bridges tracked in the FHWA National Bridge Inventory: 17.3% rated Good, 79.5% Fair, 3.1% Poor.

127
Public bridges: 17.3%
Good condition: 3.1%
Poor condition

The verdict

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

Jefferson 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 34%
lowest Poor share in state: 3.1%
Poor-condition share: 127
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.

Jefferson County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Jefferson County ranks #15 of 44 Idaho counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 3.1%). Jefferson County, Idaho contains 127 public highway bridges. Roughly 17.3% are rated “Good,” 79.5% “Fair,” and 3.1% “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

127

Public highway bridges in Jefferson County

Good condition

17.3%

22 of 127 rated 7-9

Fair condition

79.5%

101 of 127 rated 5-6

Poor condition

3.1%

4 of 127 rated 4 or below

In-state Poor-share rank

#15 of 44

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

Condition distribution

Share of 127 NBI-tracked bridges by lowest applicable component rating.

Good

17.3% (22)

Fair

79.5% (101)

Poor

3.1% (4)

Jefferson County's Poor-condition bridges carry 641 vehicle crossings a day

That is 0.2% of the county's reported daily bridge traffic on 3.1% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 160 crossings a day against 1,825 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 127 of 127 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

62.2% of Jefferson County's bridges have passed the 50-year mark

79 of the 127 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 17.3% 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 79.6% of the county's Poor-condition bridge traffic

N 4400 E (SHELTON) over BURGESS CANAL, built 1969, carries 510 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 641 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1930s

3
1940s

2
1950s

7
1960s

41
1970s

48
1980s

10
1990s

8
2000s

1
2010s

7

What this shows Construction peaked in the 1970s, when 48 of the county's bridges still in the inventory were built, which is 37.8% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year is 1973, 6 years older than the Idaho average of 1979.

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

The 5 Idaho counties nearest Jefferson County in number of bridges, with their condition splits. Its 3.1% Poor share is the 2nd-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 Jefferson 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 (this page)	127	17.3%	79.5%	3.1%	1973
Twin Falls County	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 Jefferson 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 Jefferson County, both outside Idaho so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside ID (127 bridges here).

Yuba County, CA · 127 bridges
Harrison County, IN · 127 bridges
Vermillion County, IN · 127 bridges
Knox County, KY · 127 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 127 Good 22 Fair 101 Poor 4

All bridges (127)

Sort:

STC6732;OLD HWY 91

Fair

Over: CAMAS CREEK

4.3 N. 1.0 W. HAMER, Jefferson, ID

Jefferson County Bridge Snapshot

Condition distribution

Jefferson County's Poor-condition bridges carry 641 vehicle crossings a day

62.2% of Jefferson County's bridges have passed the 50-year mark

One structure carries 79.6% of the county's Poor-condition bridge traffic

How Jefferson 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

All bridges (127)

STC6732;OLD HWY 91

BRINDLEY ROAD

STC 6743 (E 200 N)

2ND EAST STREET

STC6731;W 145 N

N 1400 E RD (ORME)

N 2900 E(HACKWART)

NORTH 4850 EAST RD

N 2900 E RD

N 3600 E RD

STC6715(N 3400 E)

N 3470 E RD

N 3980 EAST ROAD

E 1900 N

SH 48

N 3900 E; IONA RD

N 5050 E

US 20 EBL

US 20 WBL

STC 6768;N 4700 E

N YELLOWSTONE HWY

SH 48

I 15 SBL

2350 NORTH

E 700 N RD

E 421 N

N 4400 E (SHELTON)

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