US Bridges

Thorne Bay Road over Rio Roberts

Fair

Prince of Wales-Hyder Census Area, Alaska · Mile Point 5.1 · Structure no. 1456

Built
1975
50 years old
Condition
Fair
inspected July 2023
Type
Girder and Floorbeam System
Steel Continuous
Length
126 ft
3 main spans
Daily traffic
190
2020 count
Owner
State
State Highway Agency

About this bridge

Thorne Bay Road over Rio Roberts is a steel continuous girder and floorbeam system carrying Thorne Bay Road over Rio Roberts in Prince of Wales-Hyder Census Area, Alaska. It was built in 1975, so it is 50 years old, older than the Alaska average of 35.9 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 190 vehicles a day, roughly 26% of them trucks, projected to reach 230 by 2039. The structure is 126 ft (38.4 m) long and 24 ft wide. If it were closed, the detour would be 123.7 mi (199 km).

Location

Open in Google Maps
CarriesThorne Bay Road
CrossesRio Roberts
LocationMile Point 5.1
RouteState Highway 929
CountyPrince of Wales-Hyder Census Area
StateAlaska
Coordinates55.69389, -132.77583
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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJuly 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating78.4 US tons
Inventory rating47 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel Continuous
DeckWood or timber
Main spans3
Design loadHS 20
Structure length126 ft (38.4 m)
Longest span101 ft (30.8 m)
Deck width24 ft (7.4 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic190 (2020)
Projected traffic230 by 2039
Trucks26%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed123.7 mi (199 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 Thorne Bay Road over Rio Roberts built?

It was built in 1975, making it 50 years old in 2025.

What condition is Thorne Bay Road over Rio Roberts 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 2023.

How much traffic does Thorne Bay Road over Rio Roberts carry?

About 190 vehicles per day (2020 count), of which roughly 26% are trucks.

How long is Thorne Bay Road over Rio Roberts?

The structure is 126 ft (38.4 m) long with a longest span of 101 ft (30.8 m) and a deck 24 ft wide.

Who owns Thorne Bay Road over Rio Roberts?

It is owned by the State Highway Agency.