SH 21 over Boise River
GoodAda County, Idaho · Near Diversion Dam · Structure no. 000000000015769
- Built
- 1996
- 29 years old
- Condition
- Good
- inspected January 2022
- Type
- Stringer/Multi-beam or Girder
- Steel
- Length
- 1,495 ft
- 9 main spans
- Daily traffic
- 6,800
- 2023 count
- Owner
- State
- State Highway Agency
About this bridge
SH 21 over Boise River is a steel stringer/multi-beam or girder carrying SH 21 over Boise River in Ada County, Idaho. It was built in 1996, so it is 29 years old, younger 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 6,800 vehicles a day, roughly 11% of them trucks, projected to reach 10,200 by 2042. The structure is 1,495 ft (455.7 m) long and 42 ft wide. If it were closed, the detour would be 5 mi (8 km).
Location
Open in Google MapsCondition and inspection
All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.
| Component | Rating | Meaning |
|---|---|---|
| Deck | 7 Good | Some minor problems. |
| Superstructure | 7 Good | Some minor problems. |
| Substructure | 7 Good | Some minor problems. |
| Channel and channel protection | 9 Excellent | No problems noted. |
Structure
Traffic and service
Ownership and planned work
Frequently asked questions
When was SH 21 over Boise River built?
It was built in 1996, making it 29 years old in 2025.
What condition is SH 21 over Boise River 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 2022.
How much traffic does SH 21 over Boise River carry?
About 6,800 vehicles per day (2023 count), of which roughly 11% are trucks.
How long is SH 21 over Boise River?
The structure is 1,495 ft (455.7 m) long with a longest span of 185 ft (56.4 m) and a deck 42 ft wide.
Who owns SH 21 over Boise River?
It is owned by the State Highway Agency.