US Bridges

Knowles Hill Road over Brock Brook

Good

Grafton County, New Hampshire · 3.8 MI from Shin Valley · Structure no. 000300940010800

Built
1935
90 years old, rebuilt 2018
Condition
Good
inspected August 2023
Type
Slab
Wood or Timber
Length
36 ft
1 main span
Daily traffic
96
2023 count
Owner
City
City or Municipal Highway Agency

About this bridge

Knowles Hill Road over Brock Brook is a wood or timber slab carrying Knowles Hill Road over Brock Brook in Grafton County, New Hampshire. It was built in 1935 and reconstructed in 2018, so it is 90 years old, older than the New Hampshire average of 56.9 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 9 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 96 vehicles a day, projected to reach 142 by 2043. The structure is 36 ft (11 m) long and 16 ft wide. If it were closed, the detour would be 98.8 mi (159 km).

Location

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CarriesKnowles Hill Road
CrossesBrock Brook
Location3.8 MI from Shin Valley
CountyGrafton County
StateNew Hampshire
Coordinates43.63788, -71.85909
Functional classRural Local

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck9 ExcellentNo problems noted.
Superstructure9 ExcellentNo problems noted.
Substructure9 ExcellentNo problems noted.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation9: Superior to present desirable criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating59.7 US tons
Inventory rating46.1 US tons

Structure

Structure typeSlab
MaterialWood or Timber
DeckWood or timber
Main spans1
Design loadHS 25 or greater
Structure length36 ft (11 m)
Longest span32 ft (9.8 m)
Deck width16 ft (5 m)
Roadway width15 ft (4.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic96 (2023)
Projected traffic142 by 2043
Trucks0%
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed98.8 mi (159 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCity or Municipal Highway Agency
Maintained byCity or Municipal Highway Agency
Historic statusPossibly eligible for the National Register; requires further investigation
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$314,000 (2025 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was Knowles Hill Road over Brock Brook built?

It was built in 1935, making it 90 years old in 2025. It was reconstructed in 2018.

What condition is Knowles Hill Road over Brock Brook 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 August 2023.

How much traffic does Knowles Hill Road over Brock Brook carry?

About 96 vehicles per day (2023 count).

How long is Knowles Hill Road over Brock Brook?

The structure is 36 ft (11 m) long with a longest span of 32 ft (9.8 m) and a deck 16 ft wide.

Who owns Knowles Hill Road over Brock Brook?

It is owned by the City or Municipal Highway Agency.