US Bridges

I-93 NB over Mirror Lake Road

Good

Grafton County, New Hampshire · 0.24 MI Thornton Tl · Structure no. 028402020003400

Built
1970
55 years old, rebuilt 2002
Condition
Good
inspected April 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
75 ft
1 main span
Daily traffic
7,102
2023 count
Owner
State
State Highway Agency

About this bridge

I-93 NB over Mirror Lake Road is a steel stringer/multi-beam or girder carrying I-93 NB over Mirror Lake Road in Grafton County, New Hampshire. It was built in 1970 and reconstructed in 2002, so it is 55 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 good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 7,102 vehicles a day, roughly 10% of them trucks, projected to reach 10,510 by 2043. The structure is 75 ft (22.9 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 NB
CrossesMirror Lake Road
Location0.24 MI Thornton Tl
RouteInterstate 93
CountyGrafton County
StateNew Hampshire
Coordinates43.93815, -71.68811
Functional classRural Principal Arterial - Interstate

Condition and inspection

Good

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

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure8 Very GoodNo problems noted.
Substructure7 GoodSome minor problems.
Last inspectionApril 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation7: Better than present minimum criteria
Deck geometry7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating57.4 US tons
Inventory rating34.4 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20 + Mod
Structure length75 ft (22.9 m)
Longest span69 ft (21 m)
Deck width45 ft (13.7 m)
Roadway width41 ft (12.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic7,102 (2023)
Projected traffic10,510 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 NB over Mirror Lake Road built?

It was built in 1970, making it 55 years old in 2025. It was reconstructed in 2002.

What condition is I-93 NB over Mirror Lake Road 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 April 2023.

How much traffic does I-93 NB over Mirror Lake Road carry?

About 7,102 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is I-93 NB over Mirror Lake Road?

The structure is 75 ft (22.9 m) long with a longest span of 69 ft (21 m) and a deck 45 ft wide.

Who owns I-93 NB over Mirror Lake Road?

It is owned by the State Highway Agency.