US Bridges

US 87 over Irrigation Reservoir

FairPosted for load

Fergus County, Montana · 6M NW Grass Range · Structure no. P00057107+08301

Built
1939
86 years old
Condition
Fair
inspected October 2024
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
101 ft
4 main spans
Daily traffic
1,067
2023 count
Owner
State
State Highway Agency

About this bridge

US 87 over Irrigation Reservoir is a wood or timber stringer/multi-beam or girder carrying US 87 over Irrigation Reservoir in Fergus County, Montana. It was built in 1939, so it is 86 years old, older than the Montana average of 47 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. Its operating status is: posted for load restriction.

It carries about 1,067 vehicles a day, roughly 11% of them trucks, projected to reach 1,120 by 2043. The structure is 101 ft (30.7 m) long and 30 ft wide. If it were closed, the detour would be 123.7 mi (199 km).

Location

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CarriesUS 87
CrossesIrrigation Reservoir
Location6M NW Grass Range
RouteU.S. Route 87
CountyFergus County
StateMontana
Coordinates47.04767, -108.91073
Functional classRural Principal Arterial - Other

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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionOctober 2024
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating35.1 US tons
Inventory rating21.1 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans4
Design loadH 15
Structure length101 ft (30.7 m)
Longest span25 ft (7.6 m)
Deck width30 ft (9.1 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,067 (2023)
Projected traffic1,120 by 2043
Trucks11%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed123.7 mi (199 km)
TollOn a free road
National Highway SystemYes

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 US 87 over Irrigation Reservoir built?

It was built in 1939, making it 86 years old in 2025.

What condition is US 87 over Irrigation Reservoir 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 October 2024.

How much traffic does US 87 over Irrigation Reservoir carry?

About 1,067 vehicles per day (2023 count), of which roughly 11% are trucks.

How long is US 87 over Irrigation Reservoir?

The structure is 101 ft (30.7 m) long with a longest span of 25 ft (7.6 m) and a deck 30 ft wide.

Who owns US 87 over Irrigation Reservoir?

It is owned by the State Highway Agency.