Mariners Isl Blvd over Branch Marina Lagoon
San Mateo County, California · rated Fair in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- Mariners Isl Blvd over Branch Marina Lagoon in San Mateo County, California, is rated in fair condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the deck, rated 6 (satisfactory condition) on the 0-9 scale.
- It was built in 1999, making it 26 years old at the 2025 inventory.
- It carries about 2,150 vehicles a day (traffic count year 2010).
- Its listed owner is a city or municipal highway agency.
- It is one of 224 of the 361 inventoried bridges in San Mateo County rated fair (62.0%); 37 (10.2%) 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 April 2023, on a 48-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 → (37.56261, -122.28672)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 6 | 6 | Satisfactory condition |
| Superstructure | 6 | 6 | Satisfactory condition |
| Substructure | 7 | 7 | Good condition |
Bridge details
| Structure | Continuous prestressed concrete slab |
| Length | about 160 ft |
| Location | 0.1 Mi W/o Tiller Dr |
| NBI structure number | 35C0076L |
| Condition class | Fair |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | April 2023 |
| Inspection interval (item 91) | 48 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 California department of transportation.
Busiest bridges in San Mateo County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| U.S. Highway 101 over San Mateo Creek | 1928 | 236,000 | Good |
| US 101 Rollins Rd over Transmission Canal | 1928 | 232,000 | Fair |
| US 101 Mcdonnell over Millbrae Slough | 1947 | 226,000 | Fair |
| US 101 W&e Bayshr over San Francisquito Creek | 2018 | 225,800 | Good |
| Holly Street over US Highway 101 | 1954 | 201,000 | Fair |
| Whipple Avenue over US Highway 101 | 1958 | 201,000 | Good |
All bridges nearby: San Mateo County, CA bridge conditions · every bridge in San Mateo County · California bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.