Structure 2601420003800 · Merrimack County, NH

US 4 over Merrimack River

Carries US 4 over Merrimack River, Canterbury T.l..

Overall conditionGood

Set by its lowest-rated component: Substructure at 7 of 9.

How ratings work
Deck8/9 · Very Good
Superstructure8/9 · Very Good
Substructuresets the rating7/9 · Good
Channelnot part of overall6/9 · Satisfactory
0 failed4 poor6 fair9 excellent

Elevation

Side view, colored by inspection rating
SEMI-TRUCK · 72 FT593 FT OVERALL100 FT0ELEVATION · LENGTHS TO SCALE
Deck 8/9Superstructure 8/9Substructure 7/9 · sets the rating

593 ft end to end, longest span 130 ft: about 1.6 football fields. Lengths and the semi-truck on the deck are drawn to the same scale. Each part is colored by its latest inspection rating. The inventory records lengths but not heights or the layout of the shorter spans, so those are drawn as typical for a multi-beam bridge.

Built200521 years old
Length592.8 ft180.7 m
Daily traffic15,071counted 2023
Last inspectedJuly 2023every 24 months

Location

StateNew Hampshire
CountyMerrimack
LocationCanterbury T.l.
CarriesUS 4
CrossesMerrimack River
Coordinates43.28986, -71.58795

Physical Characteristics

MaterialSteel Continuous
DesignStringer/Multi-beam
Total Length592.8 ft (180.7 m)
Max Span129.9 ft (39.6 m)
Deck Width56.1 ft (17.1 m)
Deck Area3090.0 sq m
Main Spans4
Year Built2005

Traffic

Avg Daily Traffic15,071 (2023)
Truck Traffic5%
Lanes On Bridge2

Inspection & Ownership

Last InspectionJuly 2023
Inspection FrequencyEvery 24 months
OwnerState Highway Agency
Historical SignificanceBridge is not eligible for the National Register
Scour Critical8 — Stable, low risk
Structure Number002601420003800

How Bridge Ratings Work

Inspectors rate each major part of a bridge (the deck you drive on, the superstructure of beams that holds it up, and the substructure of piers and abutments beneath) on a 0–9 scale. A bridge's overall condition is its lowest of those ratings, so one deteriorated component makes the whole bridge "poor."

0Failed
1Imminent failure
2Critical
3Serious
4Poor
5Fair
6Satisfactory
7Good
8Very good
9Excellent
Good · lowest component 7–9
Fair · lowest component 5–6
Poor · lowest component 0–4

A poor rating is not a closure. It means the bridge is flagged for priority repair or replacement; bridges judged unsafe are closed or posted with weight limits. The waterway (channel) rating is reported, but it does not count toward the overall classification.

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