US Bridges

21st Ave Eastbound over Oligarchy Ditch

Fair

Boulder County, Colorado · 300 Ft. E of Daley Dr. · Structure no. LONG-21ST-VIV

Built
1975
50 years old
Condition
Fair
inspected January 2025
Type
Culvert
Concrete
Length
21 ft
1 main span
Daily traffic
4,495
2023 count
Owner
City
City or Municipal Highway Agency

About this bridge

21st Ave Eastbound over Oligarchy Ditch is a concrete culvert carrying 21st Ave Eastbound over Oligarchy Ditch in Boulder County, Colorado. It was built in 1975, so it is 50 years old, older than the Colorado average of 42.2 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 6 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 4,495 vehicles a day, roughly 4% of them trucks, projected to reach 5,394 by 2043. The structure is 21 ft (6.3 m) long and 34 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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Carries21st Ave Eastbound
CrossesOligarchy Ditch
Location300 Ft. E of Daley Dr.
RouteCity Street 0
CountyBoulder County
StateColorado
Coordinates40.1958, -105.12002
Functional classUrban Local

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Culvert6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJanuary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating40 US tons
Inventory rating36 US tons

Structure

Structure typeCulvert
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadUnknown
Structure length21 ft (6.3 m)
Longest span21 ft (6.3 m)
Deck width34 ft (10.4 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic4,495 (2023)
Projected traffic5,394 by 2043
Trucks4%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCity or Municipal Highway Agency
Maintained byCity or Municipal Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$123,000 (2021 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was 21st Ave Eastbound over Oligarchy Ditch built?

It was built in 1975, making it 50 years old in 2025.

What condition is 21st Ave Eastbound over Oligarchy Ditch in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in January 2025.

How much traffic does 21st Ave Eastbound over Oligarchy Ditch carry?

About 4,495 vehicles per day (2023 count), of which roughly 4% are trucks.

How long is 21st Ave Eastbound over Oligarchy Ditch?

The structure is 21 ft (6.3 m) long with a longest span of 21 ft (6.3 m) and a deck 34 ft wide.

Who owns 21st Ave Eastbound over Oligarchy Ditch?

It is owned by the City or Municipal Highway Agency.