US Bridges

S 21-S Main ST over Pondera Coulee

Good

Pondera County, Montana · Conrad by Fleet Supply · Structure no. P00021003+08001

Built
1934
91 years old, rebuilt 1989
Condition
Good
inspected February 2025
Type
Culvert
Steel
Length
38 ft
2 main spans
Daily traffic
1,245
2023 count
Owner
State
State Highway Agency

About this bridge

S 21-S Main ST over Pondera Coulee is a steel culvert carrying S 21-S Main ST over Pondera Coulee in Pondera County, Montana. It was built in 1934 and reconstructed in 1989, so it is 91 years old, older than the Montana average of 47 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 1,245 vehicles a day, roughly 3% of them trucks, projected to reach 1,307 by 2043. The structure is 38 ft (11.5 m) long. If it were closed, the detour would be 9.9 mi (16 km).

Location

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CarriesS 21-S Main ST
CrossesPondera Coulee
LocationConrad by Fleet Supply
RouteU.S. Route 21
CountyPondera County
StateMontana
Coordinates48.16372, -111.95012
Functional classRural Minor Arterial

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Channel and channel protection7 GoodSome minor problems.
Culvert7 GoodSome minor problems.
Last inspectionFebruary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating40 US tons
Inventory rating36 US tons

Structure

Structure typeCulvert
MaterialSteel
DeckNot applicable
Main spans2
Design loadHL 93
Structure length38 ft (11.5 m)
Longest span15 ft (4.7 m)
Deck width0 ft (0 m)
Roadway width0 ft (0 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,245 (2023)
Projected traffic1,307 by 2043
Trucks3%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed9.9 mi (16 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState 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 S 21-S Main ST over Pondera Coulee built?

It was built in 1934, making it 91 years old in 2025. It was reconstructed in 1989.

What condition is S 21-S Main ST over Pondera Coulee in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in February 2025.

How much traffic does S 21-S Main ST over Pondera Coulee carry?

About 1,245 vehicles per day (2023 count), of which roughly 3% are trucks.

How long is S 21-S Main ST over Pondera Coulee?

The structure is 38 ft (11.5 m) long with a longest span of 15 ft (4.7 m).

Who owns S 21-S Main ST over Pondera Coulee?

It is owned by the State Highway Agency.