County profile · official public datasets

Imperial County, CA

444 public highway bridges tracked in the FHWA National Bridge Inventory: 50.7% rated Good, 40.5% Fair, 8.8% Poor.

444
Public bridges: 50.7%
Good condition: 8.8%
Poor condition

The verdict

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

Imperial County posts a higher-than-median Poor-condition share among rated counties in the state across mid-size county bridge inventory.

41st
of 58 on Poor share: 8.8%
Poor-condition share: 444
public highway bridges: 1968
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.

Imperial County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Imperial County ranks #41 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 8.8%). Imperial County, California contains 444 public highway bridges. Roughly 50.7% are rated “Good,” 40.5% “Fair,” and 8.8% “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

444

Public highway bridges in Imperial County

Good condition

50.7%

225 of 444 rated 7-9

Fair condition

40.5%

180 of 444 rated 5-6

Poor condition

8.8%

39 of 444 rated 4 or below

In-state Poor-share rank

#41 of 58

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

Condition distribution

Share of 444 NBI-tracked bridges by lowest applicable component rating.

Good

50.7% (225)

Fair

40.5% (180)

Poor

8.8% (39)

Imperial County's Poor-condition bridges carry 121,885 vehicle crossings a day

That is 5.5% of the county's reported daily bridge traffic on 8.8% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 3,125 crossings a day against 6,065 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 444 of 444 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

62.4% of Imperial County's bridges have passed the 50-year mark

277 of the 444 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 50.7% 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 9.6% of the county's Poor-condition bridge traffic

FORRESTER RD (S30) over WESTSIDE MAIN CANAL, built 1950, carries 11,714 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 39-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 121,885 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1910s

1
1920s

2
1930s

44
1940s

29
1950s

77
1960s

66
1970s

103
1980s

53
1990s

42
2000s

9
2010s

15
2020s

3

What this shows Construction peaked in the 1970s, when 103 of the county's bridges still in the inventory were built, which is 23.2% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1968) matches the California average (1970).

How Imperial County compares with California's closest counties by inventory size

The 5 California counties nearest Imperial County in number of bridges, with their condition splits. Its 8.8% Poor share is the 6th-lowest of these 6. Its average build year of 1968 against a peer-group mean of 1967 is in line with the group.

Showing the 5 closest of 57 California counties eligible for comparison.

Bridge inventory size and condition shares for Imperial County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Tehama County	450	36.9%	56.2%	6.9%	1961
Imperial County (this page)	444	50.7%	40.5%	8.8%	1968
Butte County	437	31.8%	62%	6.2%	1958
Siskiyou County	421	39%	55.6%	5.5%	1971
Santa Barbara County	418	51.4%	42.8%	5.7%	1975
San Luis Obispo County	401	47.6%	46.6%	5.7%	1970

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

Similar inventory size

Nearest county inventories outside CA (444 bridges here).

Craighead County, AR · 442 bridges
Erie County, PA · 442 bridges
Loudoun County, VA · 442 bridges
Washington County, AR · 449 bridges

Similar average build year

Nearest mean year-built outside CA (1968 here).

Montgomery County, PA · avg 1968 · 828 bridges
Providence County, RI · avg 1968 · 476 bridges
Delaware County, PA · avg 1968 · 387 bridges
Genesee County, MI · avg 1968 · 371 bridges

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

All 444 Good 225 Fair 180 Poor 39

All bridges (444)

Sort:

Imperial County Bridge Snapshot

Condition distribution

Imperial County's Poor-condition bridges carry 121,885 vehicle crossings a day

62.4% of Imperial County's bridges have passed the 50-year mark

One structure carries 9.6% of the county's Poor-condition bridge traffic

How Imperial County compares with California'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 (444)

W78 - N111

STATE ROUTE 78 EB

STATE ROUTE 78 WB

STATE ROUTE 78

STATE ROUTE 98

STATE ROUTE 78 WB

STATE ROUTE 78 EB

INTERSTATE 8

DOGWOOD ROAD

STATE ROUTE 111

IMPERIAL AVENUE

STATE ROUTE 111

SCARONI ROAD

IMPERIAL AVE E

EDDINS RD

ATEN ROAD

ROSS RD

W. MAIN ST

BRANDT RD

GORDONS WELL OC

O&M Service Road

JEFFREY ROAD

SILSBEE ROAD

INTERSTATE 8 WB

DREW ROAD

FORESTER ROAD

LA BRUCHERIE ROAD

EIGHTH STREET

WESTSIDE ROAD

DERRICK ROAD

INTERSTATE 8 WB

ORCHARD ROAD

DUNAWAY ROAD

STATE ROUTE 186

INTERSTATE 8 WB

STATE ROUTE 115

INTERSTATE 8 EB

WINTERHAVEN ROAD

STATE ROUTE 78 EB

STATE ROUTE 111

ANDERHOLT ROAD

MELOLAND ROAD

BARBARA WORTH RD

BOWKER ROAD

CA State Rt S-24

67113: GRAYS WELL

BONDS CORNER ROAD

OGILBY ROAD

INTERSTATE 8 EB

STATE ROUTE 111

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