US Bridges

IRR - SR 480 over Missouri River

Fair

Richland County, Montana · 9M SW Brockton · Structure no. S00480003+00001

Built
1968
57 years old
Condition
Fair
inspected May 2023
Type
Girder and Floorbeam System
Steel Continuous
Length
1,057 ft
4 main spans
Daily traffic
80
2023 count
Owner
State
State Highway Agency

About this bridge

IRR - SR 480 over Missouri River is a steel continuous girder and floorbeam system carrying IRR - SR 480 over Missouri River in Richland County, Montana. It was built in 1968, so it is 57 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.

It carries about 80 vehicles a day, roughly 4% of them trucks, projected to reach 84 by 2043. The structure is 1,057 ft (322.1 m) long and 33 ft wide. If it were closed, the detour would be 75.8 mi (122 km).

Location

Open in Google Maps
CarriesIRR - SR 480
CrossesMissouri River
Location9M SW Brockton
RouteState Highway 480
CountyRichland County
StateMontana
Coordinates48.064, -105.0314
Functional classRural Major Collector

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.
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 inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no 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 geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating43 US tons
Inventory rating26 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans4 (+2 approach)
Design loadHS 15
Structure length1,057 ft (322.1 m)
Longest span266 ft (81 m)
Deck width33 ft (10.1 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic80 (2023)
Projected traffic84 by 2043
Trucks4%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed75.8 mi (122 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 proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$2.3 million
NavigationNo navigation control on waterway

Frequently asked questions

When was IRR - SR 480 over Missouri River built?

It was built in 1968, making it 57 years old in 2025.

What condition is IRR - SR 480 over Missouri 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 May 2023.

How much traffic does IRR - SR 480 over Missouri River carry?

About 80 vehicles per day (2023 count), of which roughly 4% are trucks.

How long is IRR - SR 480 over Missouri River?

The structure is 1,057 ft (322.1 m) long with a longest span of 266 ft (81 m) and a deck 33 ft wide.

Who owns IRR - SR 480 over Missouri River?

It is owned by the State Highway Agency.