US Bridges

County Road 84W over North St. Vrain Creek

Fair

Boulder County, Colorado · 1.0 Mile Northwest of Sta · Structure no. BC-84W-1.0-NSV

Built
1927
98 years old
Condition
Fair
inspected January 2025
Type
Tee Beam
Concrete
Length
45 ft
1 main span
Daily traffic
122
2023 count
Owner
County
County Highway Agency

About this bridge

County Road 84W over North St. Vrain Creek is a concrete tee beam carrying County Road 84W over North St. Vrain Creek in Boulder County, Colorado. It was built in 1927, so it is 98 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 5 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 122 vehicles a day, roughly 9% of them trucks, projected to reach 147 by 2043. The structure is 45 ft (13.7 m) long and 23 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesCounty Road 84W
CrossesNorth St. Vrain Creek
Location1.0 Mile Northwest of Sta
RouteCounty Highway 0
CountyBoulder County
StateColorado
Coordinates40.21848, -105.53522
Functional classRural 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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection7 GoodSome minor problems.
Last inspectionJanuary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment5: Somewhat better than minimum adequacy to tolerate being left in place as is
Operating rating50.7 US tons
Inventory rating30.4 US tons

Structure

Structure typeTee Beam
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20
Structure length45 ft (13.7 m)
Longest span40 ft (12.3 m)
Deck width23 ft (7 m)
Roadway width20 ft (6.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic122 (2023)
Projected traffic147 by 2043
Trucks9%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.9 mi (3 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty Highway Agency
Historic statusPossibly eligible for the National Register; requires further investigation
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was County Road 84W over North St. Vrain Creek built?

It was built in 1927, making it 98 years old in 2025.

What condition is County Road 84W over North St. Vrain Creek 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 County Road 84W over North St. Vrain Creek carry?

About 122 vehicles per day (2023 count), of which roughly 9% are trucks.

How long is County Road 84W over North St. Vrain Creek?

The structure is 45 ft (13.7 m) long with a longest span of 40 ft (12.3 m) and a deck 23 ft wide.

Who owns County Road 84W over North St. Vrain Creek?

It is owned by the County Highway Agency.