Idaho has 4,646 bridges on public roads, according to the FHWA National Bridge Inventory. Of those, 250 are rated in poor condition — a rate of 5.4% — below the national average of 6.7%. Another 2,928 are in fair condition, while 1,468 are in good condition.
Use the interactive Idaho bridge map below to explore every bridge, color-coded by condition. Click any cluster to zoom in, then click an individual bridge for its route, structural ratings, year built, daily traffic, and last inspection date. Filter by condition using the checkboxes, or switch to satellite view to see bridges from above. For a national comparison, see the full US bridges interactive map.
Idaho Bridge Conditions by the Numbers
- 4,646 total bridges on public roads in Idaho
- 250 in poor condition (5.4%) — below the national average of 6.7%
- 2,928 in fair condition (63%)
- 1,468 in good condition (31.6%)
- Oldest bridge in the inventory: WILDHORSE ROAD, built 1908
Oldest Bridges in Idaho
The oldest bridges in Idaho date back to the 1900s. The ten oldest Idaho bridges still in the national inventory:
| Route / Facility | Crosses | Year Built | Condition |
|---|---|---|---|
| WILDHORSE ROAD | WILDHORSE RIVER | 1908 | Poor |
| SPERRY GRADE RD | POTLATCH RVR(SPERRY BR) | 1908 | Fair |
| RAILROAD GRADE RD | ST. JOE RIVER | 1908 | Fair |
| STC 5711;MOON PASS | BIG DICK CREEK | 1909 | Poor |
| STC 5711;MOON PASS | SQUAW CREEK | 1909 | Fair |
| STC 3007;UNITY RD | WEISER RIVER | 1910 | Poor |
| POTLATCH ROAD | ELK CREEK TRESTLE | 1912 | Poor |
| POTLATCH ROAD | BIG CREEK TRESTLE | 1912 | Poor |
| POTLATCH ROAD | AGATHA CREEK TRESTLE | 1912 | Poor |
| POTLATCH ROAD | BLACK PRINCE TRESTLE | 1912 | Poor |
Most Concerning Idaho Bridges: Poor Condition and High Traffic
The bridges of greatest concern combine a poor structural rating with high daily traffic loads. These Idaho bridges carry the most vehicles per day while rated in poor condition:
| Route / Facility | Crosses | Daily Traffic | Year Built | Deck | Superstructure | Substructure |
|---|---|---|---|---|---|---|
| I 90 WBL | PEDESTRIAN/BIKE PATH | 31,250 vehicles/day | 1971 | Satisfactory (6) | Very Good (8) | Poor (4) |
| S 25 E; S HITT RD | SAND CREEK | 27,500 vehicles/day | 1994 | Good (7) | Poor (4) | Good (7) |
| NHS 7773;10TH AVE | CITY ST;UPRR;CALDWELL OP | 19,500 vehicles/day | 1956 | Satisfactory (6) | Poor (4) | Satisfactory (6) |
| STP7046;LINCOLN RD | IDAHO CANAL | 18,000 vehicles/day | 1984 | Fair (5) | Poor (4) | Satisfactory (6) |
| I 15 SBL | I15B;UPRR;S.BLACKFOOT IC | 13,750 vehicles/day | 1961 | Fair (5) | Poor (4) | Satisfactory (6) |
How Idaho Bridge Conditions Are Assessed
Bridge condition in the NBI is determined by ratings of three structural components — deck, superstructure, and substructure — on a scale of 0 (failed) to 9 (excellent). A bridge is classified as good when all three components score 7 or above. It is classified as poor when any component scores 4 or below. Ratings of 5 or 6 on any component with no component below 5 result in a fair classification. ITD coordinates inspections across Idaho in line with FHWA standards, with most bridges inspected on a 24-month cycle.
Frequently Asked Questions
How many bridges in Idaho are in poor condition?
250 of Idaho’s 4,646 bridges are currently rated in poor condition by the FHWA National Bridge Inventory, a rate of 5.4%.
What is the oldest bridge in
The oldest bridge recorded in Idaho’s NBI inventory is WILDHORSE ROAD, built in 1908.
What does a poor bridge rating mean?
A poor rating means at least one of a bridge’s three key structural components — deck, superstructure, or substructure — has been rated 4 or below on the NBI 0-9 scale. A rating of 4 is defined as “poor condition,” and ratings of 3, 2, 1, or 0 indicate increasingly serious deterioration. Poor-rated bridges are not necessarily unsafe or closed, but they require priority attention and monitoring.
View all 624,000+ US bridges on the national interactive map
Compare with neighboring states: Montana bridges map | Nevada bridges map | Oregon bridges map | Utah bridges map | Washington bridges map | Wyoming bridges map
