US Bridges

County Road 31D over Big Thompson River

Fair

Larimer County, Colorado · 0.1 MI N of CO RD 22H · Structure no. LR31D-0.1-22H

Built
1978
47 years old
Condition
Fair
inspected April 2023
Type
Tee Beam
Prestressed Concrete
Length
133 ft
3 main spans
Daily traffic
248
2023 count
Owner
County
County Highway Agency

About this bridge

County Road 31D over Big Thompson River is a prestressed concrete tee beam carrying County Road 31D over Big Thompson River in Larimer County, Colorado. It was built in 1978, so it is 47 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 248 vehicles a day, roughly 19% of them trucks, projected to reach 311 by 2042. The structure is 133 ft (40.5 m) long and 33 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesCounty Road 31D
CrossesBig Thompson River
Location0.1 MI N of CO RD 22H
RouteCounty Highway 0
CountyLarimer County
StateColorado
Coordinates40.42152, -105.22091
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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionApril 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry6: Equal to present minimum criteria
Waterway adequacy4: Meets minimum tolerable limits to be left in place as is
Approach roadway alignment8: Equal to present desirable criteria
Operating rating40 US tons
Inventory rating36 US tons

Structure

Structure typeTee Beam
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadUnknown
Structure length133 ft (40.5 m)
Longest span42 ft (12.9 m)
Deck width33 ft (10.2 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic248 (2023)
Projected traffic311 by 2042
Trucks19%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed1.2 mi (2 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 31D over Big Thompson River built?

It was built in 1978, making it 47 years old in 2025.

What condition is County Road 31D over Big Thompson River 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 April 2023.

How much traffic does County Road 31D over Big Thompson River carry?

About 248 vehicles per day (2023 count), of which roughly 19% are trucks.

How long is County Road 31D over Big Thompson River?

The structure is 133 ft (40.5 m) long with a longest span of 42 ft (12.9 m) and a deck 33 ft wide.

Who owns County Road 31D over Big Thompson River?

It is owned by the County Highway Agency.