US Bridges

I-89 SB over Silk Farm Road

Good

Merrimack County, New Hampshire · .5 MI N. of Jct. Rt. 13 · Structure no. 005201750005100

Built
1959
66 years old, rebuilt 1993
Condition
Good
inspected May 2023
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
169 ft
3 main spans
Daily traffic
20,412
2023 count
Owner
State
State Highway Agency

About this bridge

I-89 SB over Silk Farm Road is a steel continuous stringer/multi-beam or girder carrying I-89 SB over Silk Farm Road in Merrimack County, New Hampshire. It was built in 1959 and reconstructed in 1993, so it is 66 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 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 20,412 vehicles a day, roughly 6% of them trucks, projected to reach 30,209 by 2043. The structure is 169 ft (51.5 m) long and 57 ft wide. If it were closed, the detour would be 11.2 mi (18 km).

Location

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CarriesI-89 SB
CrossesSilk Farm Road
Location.5 MI N. of Jct. Rt. 13
RouteInterstate 89
CountyMerrimack County
StateNew Hampshire
Coordinates43.18271, -71.57426
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.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Last inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation7: Better than present minimum criteria
Deck geometry2: Basically intolerable, requiring high priority of replacement
Approach roadway alignment8: Equal to present desirable criteria
Operating rating110.1 US tons
Inventory rating61.7 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 25 or greater
Structure length169 ft (51.5 m)
Longest span72 ft (21.9 m)
Deck width57 ft (17.4 m)
Roadway width43 ft (13.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic20,412 (2023)
Projected traffic30,209 by 2043
Trucks6%
Lanes on structure3
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed11.2 mi (18 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-89 SB over Silk Farm Road built?

It was built in 1959, making it 66 years old in 2025. It was reconstructed in 1993.

What condition is I-89 SB over Silk Farm 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 May 2023.

How much traffic does I-89 SB over Silk Farm Road carry?

About 20,412 vehicles per day (2023 count), of which roughly 6% are trucks.

How long is I-89 SB over Silk Farm Road?

The structure is 169 ft (51.5 m) long with a longest span of 72 ft (21.9 m) and a deck 57 ft wide.

Who owns I-89 SB over Silk Farm Road?

It is owned by the State Highway Agency.