US Bridges

County Road 71 over North St. Vrain Creek

Fair

Boulder County, Colorado · 30 Feet South of US Highw · Structure no. BC-71-2.4-NSV1

Built
1991
34 years old
Condition
Fair
inspected January 2025
Type
Arch - Thru
Wood or Timber
Length
76 ft
1 main span
Daily traffic
178
2023 count
Owner
County
County Highway Agency

About this bridge

County Road 71 over North St. Vrain Creek is a wood or timber arch - thru carrying County Road 71 over North St. Vrain Creek in Boulder County, Colorado. It was built in 1991, so it is 34 years old, younger 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 178 vehicles a day, roughly 10% of them trucks, projected to reach 214 by 2043. The structure is 76 ft (23.2 m) long and 33 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

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CarriesCounty Road 71
CrossesNorth St. Vrain Creek
Location30 Feet South of US Highw
RouteCounty Highway 0
CountyBoulder County
StateColorado
Coordinates40.24778, -105.28958
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
Deck8 Very GoodNo problems noted.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure8 Very GoodNo problems noted.
Channel and channel protection8 Very GoodNo problems noted.
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 geometry7: Better than present minimum criteria
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating38.8 US tons
Inventory rating25.5 US tons

Structure

Structure typeArch - Thru
MaterialWood or Timber
DeckWood or timber
Main spans1
Design loadHS 20
Structure length76 ft (23.2 m)
Longest span67 ft (20.4 m)
Deck width33 ft (10 m)
Roadway width32 ft (9.8 m)
Vertical clearance over deck17 ft (5.2 m)

Traffic and service

Average daily traffic178 (2023)
Projected traffic214 by 2043
Trucks10%
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—
NavigationNot applicable (no waterway)

Frequently asked questions

When was County Road 71 over North St. Vrain Creek built?

It was built in 1991, making it 34 years old in 2025.

What condition is County Road 71 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 71 over North St. Vrain Creek carry?

About 178 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is County Road 71 over North St. Vrain Creek?

The structure is 76 ft (23.2 m) long with a longest span of 67 ft (20.4 m) and a deck 33 ft wide.

Who owns County Road 71 over North St. Vrain Creek?

It is owned by the County Highway Agency.