US Bridges

County Road 31 over St. Vrain Creek

Fair

Boulder County, Colorado · 0.6 Miles South of County · Structure no. BC-31-3.9A-SV

Built
1979
46 years old
Condition
Fair
inspected January 2025
Type
Tee Beam
Prestressed Concrete
Length
116 ft
2 main spans
Daily traffic
6,233
2023 count
Owner
County
County Highway Agency

About this bridge

County Road 31 over St. Vrain Creek is a prestressed concrete tee beam carrying County Road 31 over St. Vrain Creek in Boulder County, Colorado. It was built in 1979, so it is 46 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 6,233 vehicles a day, roughly 5% of them trucks, projected to reach 7,480 by 2042. The structure is 116 ft (35.3 m) long and 38 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesCounty Road 31
CrossesSt. Vrain Creek
Location0.6 Miles South of County
RouteCounty Highway 0
CountyBoulder County
StateColorado
Coordinates40.17729, -105.17814
Functional classRural Minor Arterial

Condition and inspection

Fair

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

ComponentRatingMeaning
Deck8 Very GoodNo problems noted.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
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 geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating61.8 US tons
Inventory rating28.1 US tons

Structure

Structure typeTee Beam
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length116 ft (35.3 m)
Longest span53 ft (16.3 m)
Deck width38 ft (11.7 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,233 (2023)
Projected traffic7,480 by 2042
Trucks5%
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 statusNot eligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was County Road 31 over St. Vrain Creek built?

It was built in 1979, making it 46 years old in 2025.

What condition is County Road 31 over 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 31 over St. Vrain Creek carry?

About 6,233 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is County Road 31 over St. Vrain Creek?

The structure is 116 ft (35.3 m) long with a longest span of 53 ft (16.3 m) and a deck 38 ft wide.

Who owns County Road 31 over St. Vrain Creek?

It is owned by the County Highway Agency.