Somonauk Road over W. Br. Big Rock Crk.
DeKalb County, Illinois · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- Somonauk Road over W. Br. Big Rock Crk. in DeKalb County, Illinois, is rated in fair condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the deck, rated 5 (fair condition) on the 0-9 scale.
- It was built in 1993, making it 32 years old at the 2025 inventory.
- It carries about 2,400 vehicles a day (traffic count year 2021).
- Its listed owner is the county highway agency.
- It is one of 126 of the 262 inventoried bridges in DeKalb County rated fair (48.1%); 33 (12.6%) are rated poor.
- Its traffic status in the 2025 inventory is open, no restriction (NBI item 41).
- Its condition class and component ratings are unchanged from the 2024 inventory.
- Its most recent inspection on record is dated March 2024, on a 24-month routine inspection cycle.
- A fair rating means the lowest-rated major component scores 5 or 6 on FHWA's 0-9 scale: some deterioration or minor section loss, but the structure is sound. It is the middle class, not a warning.
View this bridge on a map → (41.79885, -88.65899)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 5 | 5 | Fair condition |
| Superstructure | 5 | 5 | Fair condition |
| Substructure | 6 | 6 | Satisfactory condition |
Bridge details
| Structure | Prestressed concrete multiple box beam |
| Length | about 46 ft |
| Location | 1150N 1510E |
| NBI structure number | 019304600000000 |
| Condition class | Fair |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | March 2024 |
| Inspection interval (item 91) | 24 months |
| Scour (item 113) | 8: foundations stable, scour above the top of the footing |
Source: FHWA National Bridge Inventory, 2025 data as reported by the Illinois department of transportation.
Busiest bridges in DeKalb County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| I-88 over Stream | 1972 | 24,900 | Fair |
| I-88 over Stream | 1972 | 24,900 | Good |
| I-88 over Stream | 1972 | 24,900 | Fair |
| Peace Rd over Br Kishwaukee River | 1995 | 15,000 | Fair |
| Annie Glidden Rd. over Watson Creek | 1971 | 13,600 | Poor |
| Peace Rd over Br Kishwaukee River | 1996 | 12,800 | Fair |
All bridges nearby: DeKalb County, IL bridge conditions · every bridge in DeKalb County · Illinois bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.