County profile · official public datasets

St. Louis County, MO

912 public highway bridges tracked in the FHWA National Bridge Inventory: 29.9% rated Good, 64.7% Fair, 5.4% Poor.

912
Public bridges: 29.9%
Good condition: 5.4%
Poor condition

The verdict

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

St. Louis County pairs a top-quartile lowest Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 23%
lowest Poor share in state: 5.4%
Poor-condition share: 912
public highway bridges: 1987
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.

St. Louis County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, St. Louis County ranks #26 of 115 Missouri counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.4%). St. Louis County, Missouri contains 912 public highway bridges. Roughly 29.9% are rated “Good,” 64.7% “Fair,” and 5.4% “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

912

Public highway bridges in St. Louis County

Good condition

29.9%

273 of 912 rated 7-9

Fair condition

64.7%

590 of 912 rated 5-6

Poor condition

5.4%

49 of 912 rated 4 or below

In-state Poor-share rank

#26 of 115

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

Condition distribution

Share of 912 NBI-tracked bridges by lowest applicable component rating.

Good

29.9% (273)

Fair

64.7% (590)

Poor

5.4% (49)

St. Louis County's Poor-condition bridges carry 1,056,872 vehicle crossings a day

That is 5.3% of the county's reported daily bridge traffic on 5.4% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 21,569 crossings a day against 14,905 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 912 of 912 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

29.7% of St. Louis County's bridges have passed the 50-year mark

271 of the 912 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 29.9% 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 17.8% of the county's Poor-condition bridge traffic

IS 270 E over CST CONWAY RD, built 1964, carries 188,530 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 49-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 1,056,872 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

3
1910s

2
1920s

12
1930s

21
1940s

9
1950s

46
1960s

142
1970s

97
1980s

120
1990s

133
2000s

184
2010s

103
2020s

40

What this shows Construction peaked in the 2000s, when 184 of the county's bridges still in the inventory were built, which is 20.2% of those with a recorded year. That cohort is now 15 to 24 years old in the 2024 inventory. Its average build year is 1987, 8 years newer than the Missouri average of 1979.

How St. Louis County compares with Missouri's closest counties by inventory size

The 5 Missouri counties nearest St. Louis County in number of bridges, with their condition splits. Its 5.4% Poor share is the 3rd-lowest of these 6. Its average build year of 1987 against a peer-group mean of 1978 is 9 years newer.

Showing the 5 closest of 114 Missouri counties eligible for comparison.

Bridge inventory size and condition shares for St. Louis County and the 5 Missouri counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Jackson County	930	42.2%	52.5%	5.4%	1982
St. Louis County (this page)	912	29.9%	64.7%	5.4%	1987
Greene County	493	44.6%	50.1%	5.3%	1978
Johnson County	476	39.3%	56.3%	4.4%	1975
Jasper County	471	42%	46.9%	11%	1978
Clay County	436	38.1%	55%	6.9%	1979

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 St. Louis 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 St. Louis County, both outside Missouri so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside MO (912 bridges here).

Fresno County, CA · 916 bridges
Erie County, NY · 906 bridges
Franklin County, OH · 922 bridges
Milwaukee County, WI · 893 bridges

Similar average build year

Nearest mean year-built outside MO (1987 here).

Ellis County, TX · avg 1987 · 691 bridges
St. Louis County, MN · avg 1987 · 663 bridges
Palm Beach County, FL · avg 1987 · 610 bridges
Dane County, WI · avg 1987 · 590 bridges

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

All 912 Good 273 Fair 590 Poor 49

Fair-condition bridges (590)

Sort:

St. Louis County Bridge Snapshot

Condition distribution

St. Louis County's Poor-condition bridges carry 1,056,872 vehicle crossings a day

29.7% of St. Louis County's bridges have passed the 50-year mark

One structure carries 17.8% of the county's Poor-condition bridge traffic

How St. Louis County compares with Missouri'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 (590)

US 61 S

RP IS170E TO IS64E

IS 270 E

US 50 E

CHAMBERS RD

FERGUSON AVE

ANDREWS DR

IS 170 W

OLD HWY 141

IS 64 E

IS 64 W

BOONES CROSSING RD

RP IS170W TO MO115

MO 370 E

RP IS270W TO US67

MO 370 W

IS 70 E

N W ENTRY DR

GIST RD E

BERMUDA DR S

FEE FEE RD

JAMES S MCDONNELL

RP IS64E TO IS170W

IS 64 E

CHESTERFIELD PKWY

IS 55 S

MAY VALLEY DR

MO 367 S

OLD SMIZER MILL RD

LEFFINGWELL AVE

US 50 E

CRESCENT AVE E

GREEN VALLEY DR

MCKELVEY RD S

MO 340 E

IS 64 E

RT BA S

MO 141 S

GEYER RD S

ST PAUL RD

MO 340 E

HILLSBORO RD

MO 141 S

MO 141 N

RP IS55S TO IS255S

OR 44 E

IS 44 W

IS 270 E

RP N HANLEY RD TO

MO 364 W

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