Middle Rd over Estero De San Antonio
Marin County, California · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- Middle Rd over Estero De San Antonio in Marin County, California, is rated in fair condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the substructure, rated 5 (fair condition) on the 0-9 scale.
- It was built in 1958, making it 67 years old at the 2025 inventory.
- It carries about 40 vehicles a day (traffic count year 1973).
- Its listed owner is the county highway agency.
- It is one of 100 of the 207 inventoried bridges in Marin County rated fair (48.3%); 16 (7.7%) are rated poor.
- 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 → (38.26393, -122.92732)
Component ratings
| Component | Rating (2025) | FHWA scale meaning |
|---|---|---|
| Deck | 6 | Satisfactory condition |
| Superstructure | 6 | Satisfactory condition |
| Substructure | 5 | Fair condition |
Bridge details
| Structure | Continuous concrete slab |
| Length | about 195 ft |
| Location | 4.5 Mi From S.R. 1 |
| NBI structure number | 27C0124 |
| Condition class | Fair |
Source: FHWA National Bridge Inventory, 2025 data as reported by the California department of transportation.
Busiest bridges in Marin County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| US Highway 101 over North San Pedro Road | 1979 | 180,000 | Fair |
| U.S. Highway 101 over Lincoln Ave-n101 on Ramp | 1938 | 180,000 | Fair |
| U.S. Highway 101 over Linden Lane | 1947 | 173,000 | Good |
| U.S. Highway 101 over Ggt Bellam Andersen | 1958 | 172,000 | Good |
| U.S. Highway 101 over Corte Madera CR & Sfd Bl | 1957 | 172,000 | Fair |
| U.S. Highway 101 over Wornum Drive | 1929 | 172,000 | Good |
All bridges nearby: Marin County, CA bridge conditions · every bridge in Marin County · California bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.