US Bridges

NH175 over Mad River

Fair

Grafton County, New Hampshire · 6.6 MI N JCT US 3 · Structure no. 003501530014700

Built
1927
98 years old
Condition
Fair
inspected May 2024
Type
Arch - Deck
Concrete
Length
86 ft
1 main span
Daily traffic
2,020
2023 count
Owner
State
State Highway Agency

About this bridge

NH175 over Mad River is a concrete arch - deck carrying NH175 over Mad River in Grafton County, New Hampshire. It was built in 1927, so it is 98 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 5 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 2,020 vehicles a day, roughly 10% of them trucks, projected to reach 2,989 by 2043. The structure is 86 ft (26.2 m) long and 28 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesNH175
CrossesMad River
Location6.6 MI N JCT US 3
RouteState Highway 175
CountyGrafton County
StateNew Hampshire
Coordinates43.86173, -71.63228
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.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMay 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment3: Basically intolerable, requiring high priority of corrective action
Operating rating36.4 US tons
Inventory rating21.8 US tons

Structure

Structure typeArch - Deck
MaterialConcrete
DeckNot applicable
Main spans1
Design loadH 15
Structure length86 ft (26.2 m)
Longest span86 ft (26.2 m)
Deck width28 ft (8.6 m)
Roadway width22 ft (6.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,020 (2023)
Projected traffic2,989 by 2043
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed1.9 mi (3 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusEligible for the National Register of Historic Places
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 Mad River built?

It was built in 1927, making it 98 years old in 2025.

What condition is NH175 over Mad River 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 May 2024.

How much traffic does NH175 over Mad River carry?

About 2,020 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is NH175 over Mad River?

The structure is 86 ft (26.2 m) long with a longest span of 86 ft (26.2 m) and a deck 28 ft wide.

Who owns NH175 over Mad River?

It is owned by the State Highway Agency.