US Bridges

I-93 SB over NH175

Fair

Grafton County, New Hampshire · 2.57 MI Thornton Tl · Structure no. 028402030008100

Built
1972
53 years old, rebuilt 2009
Condition
Fair
inspected April 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
85 ft
1 main span
Daily traffic
7,166
2023 count
Owner
State
State Highway Agency

About this bridge

I-93 SB over NH175 is a steel stringer/multi-beam or girder carrying I-93 SB over NH175 in Grafton County, New Hampshire. It was built in 1972 and reconstructed in 2009, so it is 53 years old, younger 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 7,166 vehicles a day, roughly 10% of them trucks, projected to reach 10,605 by 2043. The structure is 85 ft (25.9 m) long and 45 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesI-93 SB
CrossesNH175
Location2.57 MI Thornton Tl
RouteInterstate 93
CountyGrafton County
StateNew Hampshire
Coordinates43.97038, -71.67514
Functional classRural Principal Arterial - Interstate

Condition and inspection

Fair

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

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionApril 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating54.9 US tons
Inventory rating32.8 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20 + Mod
Structure length85 ft (25.9 m)
Longest span80 ft (24.4 m)
Deck width45 ft (13.7 m)
Roadway width40 ft (12.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic7,166 (2023)
Projected traffic10,605 by 2043
Trucks10%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible 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)
NavigationNot applicable (no waterway)

Frequently asked questions

When was I-93 SB over NH175 built?

It was built in 1972, making it 53 years old in 2025. It was reconstructed in 2009.

What condition is I-93 SB over NH175 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 2023.

How much traffic does I-93 SB over NH175 carry?

About 7,166 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is I-93 SB over NH175?

The structure is 85 ft (25.9 m) long with a longest span of 80 ft (24.4 m) and a deck 45 ft wide.

Who owns I-93 SB over NH175?

It is owned by the State Highway Agency.