Knowles Hill Road over Brock Brook
Grafton County, New Hampshire · rated Good in the 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
- Knowles Hill Road over Brock Brook in Grafton County, New Hampshire, is rated in good condition in the 2025 National Bridge Inventory (as of ).
- Its lowest-rated component is the deck, rated 9 (excellent condition) on the 0-9 scale.
- It was built in 1935 and reconstructed in 2018, making it 90 years old at the 2025 inventory.
- It carries about 96 vehicles a day (traffic count year 2023).
- Its listed owner is a city or municipal highway agency.
- It is one of 262 of the 547 inventoried bridges in Grafton County rated good (47.9%); 43 (7.9%) 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 August 2023, on a 24-month routine inspection cycle.
- A good rating means every major component - deck, superstructure, substructure, or culvert - is rated 7 or higher on FHWA's 0-9 scale: no more than minor problems.
View this bridge on a map → (43.63788, -71.85909)
Component ratings
| Component | Rating (2024) | Rating (2025) | FHWA scale meaning |
|---|---|---|---|
| Deck | 9 | 9 | Excellent condition |
| Superstructure | 9 | 9 | Excellent condition |
| Substructure | 9 | 9 | Excellent condition |
Bridge details
| Structure | Timber slab |
| Length | about 36 ft |
| Location | 3.8 Mi From Shin Valley |
| NBI structure number | 000300940010800 |
| Condition class | Good |
| Traffic status (item 41) | Open, no restriction |
| Last inspection (item 90) | August 2023 |
| 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 New Hampshire department of transportation.
Busiest bridges in Grafton County
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| I-89 NB over Plaza Connector Road | 2012 | 28,690 | Fair |
| I-89 Nh 10 over Brook Atv Trail | 1959 | 25,062 | Fair |
| I-89 Nh 10 NB over Truck Road Mascoma River | 1966 | 23,084 | Fair |
| I-89 NB over US 4 Nh 10 | 1966 | 22,727 | Good |
| I-89 NB over Connecticut River Necrr | 1966 | 22,288 | Poor |
| I-89 Nh 10 SB over US 4 | 1966 | 21,937 | Good |
All bridges nearby: Grafton County, NH bridge conditions · every bridge in Grafton County · New Hampshire bridges.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.