County profile · official public datasets

Gem County, ID

57 public highway bridges tracked in the FHWA National Bridge Inventory: 28.1% rated Good, 70.2% Fair, 1.8% Poor.

57
Public bridges: 28.1%
Good condition: 1.8%
Poor condition

The verdict

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

Gem County posts a top-quartile lowest Poor-condition share among rated counties in the state across rated county bridge inventory.

Top 20%
lowest Poor share in state: 1.8%
Poor-condition share: 57
public highway bridges: 1976
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.

Gem County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Gem County ranks #9 of 44 Idaho counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 1.8%). Gem County, Idaho contains 57 public highway bridges. Roughly 28.1% are rated “Good,” 70.2% “Fair,” and 1.8% “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

Public highway bridges in Gem County

Good condition

28.1%

16 of 57 rated 7-9

Fair condition

70.2%

40 of 57 rated 5-6

Poor condition

1.8%

1 of 57 rated 4 or below

In-state Poor-share rank

#9 of 44

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

Condition distribution

Share of 57 NBI-tracked bridges by lowest applicable component rating.

Good

28.1% (16)

Fair

70.2% (40)

Poor

1.8% (1)

Gem County's Poor-condition bridges carry 50 vehicle crossings a day

That is 0.1% of the county's reported daily bridge traffic on 1.8% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 50 crossings a day against 1,742 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 56 of 57 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

56.1% of Gem County's bridges have passed the 50-year mark

32 of the 57 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 28.1% 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 100% of the county's Poor-condition bridge traffic

LITTLE ROCK ROAD over NOBLE DRAIN, built 1955, carries 50 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 1-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 50 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

1
1930s

1
1940s

2
1950s

8
1960s

13
1970s

12
1980s

3
1990s

6
2000s

5
2010s

5
2020s

1

What this shows Construction peaked in the 1960s, when 13 of the county's bridges still in the inventory were built, which is 22.8% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1976) matches the Idaho average (1979).

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

The 5 Idaho counties nearest Gem County in number of bridges, with their condition splits. Its 1.8% Poor share is the 2nd-lowest of these 6. Its average build year of 1976 against a peer-group mean of 1976 is in line with the group.

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

Bridge inventory size and condition shares for Gem County and the 5 Idaho counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Minidoka County	66	28.8%	71.2%	0%	1983
Payette County	65	13.8%	81.5%	4.6%	1970
Camas County	61	27.9%	62.3%	9.8%	1978
Gem County (this page)	57	28.1%	70.2%	1.8%	1976
Lincoln County	53	18.9%	58.5%	22.6%	1973
Owyhee County	48	31.3%	60.4%	8.3%	1975

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 Gem 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 Gem County, both outside Idaho so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside ID (57 bridges here).

Summit County, CO · 57 bridges
DeSoto County, FL · 57 bridges
Dodge County, GA · 57 bridges
McIntosh County, GA · 57 bridges

Similar average build year

Nearest mean year-built outside ID (1976 here).

Marion County, IN · avg 1976 · 958 bridges
Mohave County, AZ · avg 1976 · 641 bridges
Comanche County, OK · avg 1976 · 593 bridges
Prince George's County, MD · avg 1976 · 576 bridges

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

All 57 Good 16 Fair 40 Poor 1

All bridges (57)

Sort:

Gem County Bridge Snapshot

Condition distribution

Gem County's Poor-condition bridges carry 50 vehicle crossings a day

56.1% of Gem County's bridges have passed the 50-year mark

One structure carries 100% of the county's Poor-condition bridge traffic

How Gem 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 (57)

STC 3842;STAR LANE

PERKINS LANE

W 2ND STREET

STC 8001;MAIN ST

STC3830;W ID BLVD

FULLER ROAD

STC9584;CHERRY LN

FROZEN DOG ROAD

BOWMAN ROAD

STC 3833;DEWEY RD

STC3831;LTL FRZOUT

CASCADE ROAD

RAMMAGE MEADOWS RD

BISHOP ROAD

STC3830;IDAHO BLVD

STC 3838;PLAZA RD

STC3842;OLD FRZOUT

STC3840; SWEET-OLA

STC 3840;SWEET-OLA

W SOUTH SLOPE RD

STC3833;EL PASO RD

WARDWELL STREET

E. 12TH STREET

BUTTE ROAD

STC9589;SALES YARD

MONTOUR ROAD

GEM ISLND S ACCESS

STC7408;W 12TH ST

STC7409;W 4TH ST

SH 16

VAN DEUSEN RD

COUNTY LINE ROAD

SH 52

SH 52

SH 52

SH 52

COUNTY LINE ROAD

MILL ROAD

LITTLE ROCK ROAD

HILLVIEW ROAD

RAMMAGE MEADOWS RD

TAMARACK FLAT ROAD

STC3840;2ND FORK

NESBITT LANE

SPUR 653C

N. BOISE AVE

STC 3840;SWEET-OLA

BISHOP ROAD

SH 52

SMA7190;SUBSTATION

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