Lanphere Road over Mad River Slough
GoodHumboldt County, California · 2.5 MI West of SR 101 · Structure no. 04C0023
- Built
- 1988
- 37 years old
- Condition
- Good
- inspected June 2023
- Type
- Stringer/Multi-beam or Girder
- Prestressed Concrete Continuous
- Length
- 232 ft
- 3 main spans
- Daily traffic
- 45
- 2011 count
- Owner
- County
- County Highway Agency
About this bridge
Lanphere Road over Mad River Slough is a prestressed concrete continuous stringer/multi-beam or girder carrying Lanphere Road over Mad River Slough in Humboldt County, California. It was built in 1988, so it is 37 years old, younger than the California average of 54.8 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 45 vehicles a day, roughly 2% of them trucks, projected to reach 69 by 2045. The structure is 232 ft (70.7 m) long and 15 ft wide. If it were closed, the detour would be 123.7 mi (199 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 | 7 Good | Some minor problems. |
Structure
Traffic and service
Ownership and planned work
Frequently asked questions
When was Lanphere Road over Mad River Slough built?
It was built in 1988, making it 37 years old in 2025.
What condition is Lanphere Road over Mad River Slough 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 June 2023.
How much traffic does Lanphere Road over Mad River Slough carry?
About 45 vehicles per day (2011 count), of which roughly 2% are trucks.
How long is Lanphere Road over Mad River Slough?
The structure is 232 ft (70.7 m) long with a longest span of 77 ft (23.4 m) and a deck 15 ft wide.
Who owns Lanphere Road over Mad River Slough?
It is owned by the County Highway Agency.