County profile · official public datasets

Boulder County, CO

311 public highway bridges tracked in the FHWA National Bridge Inventory: 34.4% rated Good, 63.3% Fair, 2.3% Poor.

311
Public bridges: 34.4%
Good condition: 2.3%
Poor condition

The verdict

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

Boulder County pairs a better-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 27%
lowest Poor share in state: 2.3%
Poor-condition share: 311
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.

Boulder County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Boulder County ranks #17 of 64 Colorado counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 2.3%). Boulder County, Colorado contains 311 public highway bridges. Roughly 34.4% are rated “Good,” 63.3% “Fair,” and 2.3% “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

311

Public highway bridges in Boulder County

Good condition

34.4%

107 of 311 rated 7-9

Fair condition

63.3%

197 of 311 rated 5-6

Poor condition

2.3%

7 of 311 rated 4 or below

In-state Poor-share rank

#17 of 64

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

Condition distribution

Share of 311 NBI-tracked bridges by lowest applicable component rating.

Good

34.4% (107)

Fair

63.3% (197)

Poor

2.3% (7)

Boulder County's Poor-condition bridges carry 54,399 vehicle crossings a day

That is 1.7% of the county's reported daily bridge traffic on 2.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 7,771 crossings a day against 9,208 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 310 of 311 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

26.4% of Boulder County's bridges have passed the 50-year mark

82 of the 311 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 34.4% 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 33.1% of the county's Poor-condition bridge traffic

US 36 ML WBND over BOULDER CREEK, built 1952, carries 18,000 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 7-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 54,399 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1910s

2
1920s

4
1930s

6
1940s

4
1950s

21
1960s

21
1970s

42
1980s

55
1990s

56
2000s

43
2010s

51
2020s

6

What this shows Construction peaked in the 1990s, when 56 of the county's bridges still in the inventory were built, which is 18% of those with a recorded year. That cohort is now 25 to 34 years old in the 2024 inventory. Its average build year is 1987, 5 years newer than the Colorado average of 1982.

How Boulder County compares with Colorado's closest counties by inventory size

The 5 Colorado counties nearest Boulder County in number of bridges, with their condition splits. Its 2.3% Poor share is the 2nd-lowest of these 6. Its average build year of 1987 against a peer-group mean of 1980 is 7 years newer.

Showing the 5 closest of 63 Colorado counties eligible for comparison.

Bridge inventory size and condition shares for Boulder County and the 5 Colorado counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Arapahoe County	391	26.1%	66.8%	7.2%	1984
Mesa County	319	35.1%	63.3%	1.6%	1981
Boulder County (this page)	311	34.4%	63.3%	2.3%	1987
Pueblo County	264	29.5%	65.9%	4.5%	1973
Douglas County	263	57.8%	39.9%	2.3%	1996
Las Animas County	207	26.1%	59.9%	14%	1968

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

Similar inventory size

Nearest county inventories outside CO (311 bridges here).

Madison County, MS · 311 bridges
Bronx County, NY · 311 bridges
Huron County, OH · 311 bridges
Saline County, NE · 312 bridges

Similar average build year

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

St. Louis County, MO · avg 1987 · 912 bridges
Ellis County, TX · avg 1987 · 691 bridges
St. Louis County, MN · avg 1987 · 663 bridges
Palm Beach County, FL · avg 1987 · 610 bridges

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

All 311 Good 107 Fair 197 Poor 7

Good-condition bridges (107)

Sort:

Boulder County Bridge Snapshot

Condition distribution

Boulder County's Poor-condition bridges carry 54,399 vehicle crossings a day

26.4% of Boulder County's bridges have passed the 50-year mark

One structure carries 33.1% of the county's Poor-condition bridge traffic

How Boulder County compares with Colorado's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

Good-condition bridges (107)

NFSR 112.0

S. Pratt Parkway

US 287 ML

SH 7 ML

Second Avenue

US 287 ML

N 63rd St (CR39)

Mountain Dr.

County Road 1

30th Street

Airport Road

Co Rd 3 / 119th S

US 287 ML

Broadway

Lefthand Canyon Dr

Monarch Road

Co Rd 39 (65th St)

Fairways Drive

Golf Club Drive

Golf Club Drive

Wildwood Road

48th CT

Mohawk Drive

Aurora Avenue

27th Street

34th Street

Gilpin Drive

Valmont Road

48th Street

EB US 36 OFF RAMP

Harvard Street

Sunset Street

96th Street

Kalmia Avenue

US 36 ML

Niwot Road CR34

Grandview Meadow D

N. 95th St (CR19)

N. 95th St (CR10)

US 36 ML

Marshall Rd(Cr 51)

83rd St (CO Rd 23)

Marshall Road

US 36 ML

County Road 94

US 36 ML

McConnell Dr.

Iris Avenue/34 St

US 36 ML

N 49th St (Cr 51)

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