US Bridges

SH 55 over Boise River;s.Channel

Good

Ada County, Idaho · 1.4 S. Eagle · Structure no. 000000000015175

Built
1978
47 years old, rebuilt 1998
Condition
Good
inspected January 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
123 ft
2 main spans
Daily traffic
45,000
2023 count
Owner
State
State Highway Agency

About this bridge

SH 55 over Boise River;s.Channel is a prestressed concrete stringer/multi-beam or girder carrying SH 55 over Boise River;s.Channel in Ada County, Idaho. It was built in 1978 and reconstructed in 1998, so it is 47 years old, older than the Idaho average of 45.3 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 45,000 vehicles a day, roughly 3% of them trucks, projected to reach 67,500 by 2042. The structure is 123 ft (37.5 m) long and 86 ft wide. If it were closed, the detour would be 9.9 mi (16 km).

CarriesSH 55
CrossesBoise River;s.Channel
Location1.4 S. Eagle
RouteState Highway 55
StateIdaho
Coordinates43.67494, -116.35425
Functional classUrban Other Principal Arterial

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure8 Very GoodNo problems noted.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionJanuary 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation7: Better than present minimum criteria
Deck geometry9: Superior to present desirable criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating53 US tons
Inventory rating31 US tons

Structure

MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length123 ft (37.5 m)
Longest span59 ft (18.1 m)
Deck width86 ft (26.2 m)
Roadway width83 ft (25.4 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic45,000 (2023)
Projected traffic67,500 by 2042
Trucks3%
Lanes on structure5
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed9.9 mi (16 km)
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusHistorical significance not determinable at this time
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was SH 55 over Boise River;s.Channel built?

It was built in 1978, making it 47 years old in 2025. It was reconstructed in 1998.

What condition is SH 55 over Boise River;s.Channel in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in January 2024.

How much traffic does SH 55 over Boise River;s.Channel carry?

About 45,000 vehicles per day (2023 count), of which roughly 3% are trucks.

How long is SH 55 over Boise River;s.Channel?

The structure is 123 ft (37.5 m) long with a longest span of 59 ft (18.1 m) and a deck 86 ft wide.

Who owns SH 55 over Boise River;s.Channel?

It is owned by the State Highway Agency.