US Bridges

Durnam Road over Gallatin River

FairPosted for load

Gallatin County, Montana · Durnam Bridge · Structure no. 011106000000077

Built
1970
55 years old, rebuilt 1995
Condition
Fair
inspected July 2024
Type
Truss - Thru
Steel
Length
76 ft
1 main span
Daily traffic
99
Owner
Federal
U.S. Forest Service

About this bridge

Durnam Road over Gallatin River is a steel truss - thru carrying Durnam Road over Gallatin River in Gallatin County, Montana. It was built in 1970 and reconstructed in 1995, so it is 55 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 99 vehicles a day, projected to reach 148 by 2045. The structure is 76 ft (23.2 m) long and 18 ft wide. If it were closed, the detour would be 98.2 mi (158 km).

Location

Open in Google Maps
CarriesDurnam Road
CrossesGallatin River
LocationDurnam Bridge
RouteFederal Lands Road 3120
CountyGallatin County
StateMontana
Coordinates45.32366, -111.17511
Functional classRural Local

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.
Substructure7 GoodSome minor problems.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionJuly 2024
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourFoundations stable; action required to protect exposed foundations
Structural evaluation3: Basically intolerable, requiring high priority of corrective action
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment3: Basically intolerable, requiring high priority of corrective action
Operating rating14.7 US tons
Inventory rating11 US tons

Structure

Structure typeTruss - Thru
MaterialSteel
DeckWood or timber
Main spans1
Design loadUnknown
Structure length76 ft (23.2 m)
Longest span76 ft (23.2 m)
Deck width18 ft (5.5 m)
Roadway width16 ft (4.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic99 (—)
Projected traffic148 by 2045
Trucks—
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed98.2 mi (158 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerU.S. Forest Service
Maintained byU.S. Forest Service
Historic statusHistorical significance not determinable at this time
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was Durnam Road over Gallatin River built?

It was built in 1970, making it 55 years old in 2025. It was reconstructed in 1995.

What condition is Durnam Road over Gallatin 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 July 2024.

How much traffic does Durnam Road over Gallatin River carry?

About 99 vehicles per day (latest count).

How long is Durnam Road over Gallatin River?

The structure is 76 ft (23.2 m) long with a longest span of 76 ft (23.2 m) and a deck 18 ft wide.

Who owns Durnam Road over Gallatin River?

It is owned by the U.S. Forest Service.