US Bridges

NH175 over Mill Brook

Fair

Grafton County, New Hampshire · 2.85 Mi. N. of Campton Tl · Structure no. 025402030008800

Built
1935
90 years old, rebuilt 1979
Condition
Fair
inspected April 2024
Type
Tee Beam
Concrete
Length
41 ft
1 main span
Daily traffic
1,610
2023 count
Owner
State
State Highway Agency

About this bridge

NH175 over Mill Brook is a concrete tee beam carrying NH175 over Mill Brook in Grafton County, New Hampshire. It was built in 1935 and reconstructed in 1979, 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 fair condition with a lowest component rating of 6 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 1,610 vehicles a day, roughly 10% of them trucks, projected to reach 2,382 by 2043. The structure is 41 ft (12.5 m) long and 28 ft wide. If it were closed, the detour would be 8.1 mi (13 km).

Location

Open in Google Maps
CarriesNH175
CrossesMill Brook
Location2.85 Mi. N. of Campton Tl
RouteState Highway 175
CountyGrafton County
StateNew Hampshire
Coordinates43.90191, -71.66705
Functional classRural Minor Collector

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionApril 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating25 US tons
Inventory rating18 US tons

Structure

Structure typeTee Beam
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadH 10
Structure length41 ft (12.5 m)
Longest span38 ft (11.6 m)
Deck width28 ft (8.6 m)
Roadway width25 ft (7.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,610 (2023)
Projected traffic2,382 by 2043
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed8.1 mi (13 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState 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 NH175 over Mill Brook built?

It was built in 1935, making it 90 years old in 2025. It was reconstructed in 1979.

What condition is NH175 over Mill Brook in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in April 2024.

How much traffic does NH175 over Mill Brook carry?

About 1,610 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is NH175 over Mill Brook?

The structure is 41 ft (12.5 m) long with a longest span of 38 ft (11.6 m) and a deck 28 ft wide.

Who owns NH175 over Mill Brook?

It is owned by the State Highway Agency.