US Bridges

S 359 over South Boulder River

Fair

Madison County, Montana · 3M S Jefferson Island · Structure no. S00359006+02091

Built
1958
67 years old
Condition
Fair
inspected September 2024
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
50 ft
2 main spans
Daily traffic
1,429
2023 count
Owner
State
State Highway Agency

About this bridge

S 359 over South Boulder River is a wood or timber stringer/multi-beam or girder carrying S 359 over South Boulder River in Madison County, Montana. It was built in 1958, so it is 67 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 1,429 vehicles a day, roughly 5% of them trucks, projected to reach 1,579 by 2043. The structure is 50 ft (15.2 m) long and 26 ft wide. If it were closed, the detour would be 46 mi (74 km).

Location

Open in Google Maps
CarriesS 359
CrossesSouth Boulder River
Location3M S Jefferson Island
RouteState Highway 359
CountyMadison County
StateMontana
Coordinates45.8057, -111.92782
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
Deck7 GoodSome minor problems.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionSeptember 2024
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 geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating54 US tons
Inventory rating38 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans2
Design loadHS 15
Structure length50 ft (15.2 m)
Longest span25 ft (7.6 m)
Deck width26 ft (7.9 m)
Roadway width25 ft (7.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,429 (2023)
Projected traffic1,579 by 2043
Trucks5%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed46 mi (74 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 359 over South Boulder River built?

It was built in 1958, making it 67 years old in 2025.

What condition is S 359 over South Boulder 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 September 2024.

How much traffic does S 359 over South Boulder River carry?

About 1,429 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is S 359 over South Boulder River?

The structure is 50 ft (15.2 m) long with a longest span of 25 ft (7.6 m) and a deck 26 ft wide.

Who owns S 359 over South Boulder River?

It is owned by the State Highway Agency.