US Bridges

I-93 US 4 SB over Merrimack River

Fair

Merrimack County, New Hampshire · 1.5 MI N. JCT RT3 · Structure no. 005201360011600

Built
1959
66 years old, rebuilt 1988
Condition
Fair
inspected August 2024
Type
Girder and Floorbeam System
Steel Continuous
Length
524 ft
3 main spans
Daily traffic
25,801
2023 count
Owner
State
State Highway Agency

About this bridge

I-93 US 4 SB over Merrimack River is a steel continuous girder and floorbeam system carrying I-93 US 4 SB over Merrimack River in Merrimack County, New Hampshire. It was built in 1959 and reconstructed in 1988, 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 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 25,801 vehicles a day, roughly 6% of them trucks, projected to reach 38,185 by 2043. The structure is 524 ft (159.7 m) long and 52 ft wide.

Location

Open in Google Maps
CarriesI-93 US 4 SB
CrossesMerrimack River
Location1.5 MI N. JCT RT3
RouteInterstate 93
CountyMerrimack County
StateNew Hampshire
Coordinates43.22949, -71.53643
Functional classUrban 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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
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 inspectionAugust 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry9: Superior to present desirable criteria
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating56 US tons
Inventory rating33.5 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20 + Mod
Structure length524 ft (159.7 m)
Longest span188 ft (57.3 m)
Deck width52 ft (15.8 m)
Roadway width48 ft (14.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic25,801 (2023)
Projected traffic38,185 by 2043
Trucks6%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesWaterway
Detour if closed—
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)
NavigationNo navigation control on waterway

Frequently asked questions

When was I-93 US 4 SB over Merrimack River built?

It was built in 1959, making it 66 years old in 2025. It was reconstructed in 1988.

What condition is I-93 US 4 SB over Merrimack 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 August 2024.

How much traffic does I-93 US 4 SB over Merrimack River carry?

About 25,801 vehicles per day (2023 count), of which roughly 6% are trucks.

How long is I-93 US 4 SB over Merrimack River?

The structure is 524 ft (159.7 m) long with a longest span of 188 ft (57.3 m) and a deck 52 ft wide.

Who owns I-93 US 4 SB over Merrimack River?

It is owned by the State Highway Agency.