US Bridges

US 89 over Mill Coulee Creek

Fair

Cascade County, Montana · 1M NE Sun River · Structure no. P00003008+08371

Built
1940
85 years old
Condition
Fair
inspected October 2024
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
76 ft
4 main spans
Daily traffic
1,437
2023 count
Owner
State
State Highway Agency

About this bridge

US 89 over Mill Coulee Creek is a wood or timber stringer/multi-beam or girder carrying US 89 over Mill Coulee Creek in Cascade County, Montana. It was built in 1940, so it is 85 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 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 1,437 vehicles a day, roughly 4% of them trucks, projected to reach 1,509 by 2043. The structure is 76 ft (23.2 m) long and 30 ft wide. If it were closed, the detour would be 18 mi (29 km).

Location

Open in Google Maps
CarriesUS 89
CrossesMill Coulee Creek
Location1M NE Sun River
RouteU.S. Route 89
CountyCascade County
StateMontana
Coordinates47.54463, -111.71056
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
Deck7 GoodSome minor problems.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionOctober 2024
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 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 rating41 US tons
Inventory rating29 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans4
Design loadH 15
Structure length76 ft (23.2 m)
Longest span19 ft (5.8 m)
Deck width30 ft (9.1 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,437 (2023)
Projected traffic1,509 by 2043
Trucks4%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed18 mi (29 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 US 89 over Mill Coulee Creek built?

It was built in 1940, making it 85 years old in 2025.

What condition is US 89 over Mill Coulee 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 October 2024.

How much traffic does US 89 over Mill Coulee Creek carry?

About 1,437 vehicles per day (2023 count), of which roughly 4% are trucks.

How long is US 89 over Mill Coulee Creek?

The structure is 76 ft (23.2 m) long with a longest span of 19 ft (5.8 m) and a deck 30 ft wide.

Who owns US 89 over Mill Coulee Creek?

It is owned by the State Highway Agency.